The following is a timeline of the Syrian uprising from September to December 2011. This period saw the uprising take on many of the characteristics of a civil war, according to several outside observers, including the United Nations Commission on Human Rights, as armed elements became better organized and began carrying out successful attacks in retaliation for the ongoing crackdown by the Syrian government on demonstrators and defectors.

September 2011

1 September

The attorney general of Hama resigned. According to the Syrian Observatory for Human Rights, Syrian Army elements laid siege to Douma, a Damascus suburb, and killed a man in the central city of Homs. It claimed 360 civilians and 113 security officers were killed during the Ramadan crackdown of the previous month. Syrian troops reportedly conducted house-to-house searches in Hama.

3 September

Syrian army's fighter jets flew over Houla and Rastan. There were also reports that the Syrian army were deployed in Banyas and raided Tal Kalakh and regions of Deir az-Zour. Al-Arabiya also reported that several protests broke out in the country, adding that "thousands participated in the funeral of martyrs of Arbin, near Damascus."

4 September

Syrian activists said at least 13 people have been killed by the Syrian army during protests. The reported deaths came as the head of the International Committee of the Red Cross (ICRC) was due to meet with senior Syrian officials in the capital, Damascus. Eight of the deaths occurred in the Idlib province in the country's northwestern area, the Local Co-ordination Committees (LCC) said.

State-run media claimed 5 soldiers, one army officer, and 3 civilians were killed when "terrorists" attacked a military bus in Mhardeh in the morning. The report said 3 of the "terrorists" were killed in a shootout, while one loyalist soldier and another gunman were injured.

6 September Activists stated that Syrian security forces had killed two people as armoured vehicles came through the streets. Two mechanics were killed at their workplace in the town of al-Restan near Homs, the Local Coordination Committee said. City residents were hiding in homes and offices to escape the gunfire, while armoured vehicles were "shooting toward anything moving", the LCC said, citing witnesses on the ground.

Ban Ki-moon, the United Nations secretary-general, made his strongest remarks yet on the crackdown under way against Syrian anti-government protesters. Ban Ki-moon condemned the violence, which he said was being committed by President Bashar al-Assad's government. Ban called on Assad to take "bold and decisive measures before it's too late". "It's already too late, in fact," Ban said in New Zealand, where he was attending a meeting of Pacific leaders. "If it takes more and more days, then more people will be killed.", he went on to say. Ban also stated that it was time for United Nation members to unite and take "coherent measures".

Aleppo also witnessed a major demonstration after the sudden death of prominent Aleppine scholar and government critic Ibrahim Salqini, though state-run media claimed he died of a heart attack. Tens of thousands of people attended his funeral march and chanted against the government, invoking revolutionary slogans such as "better death than humiliation", before security forces reportedly fired on them as they entered the city cemetery.

7 September

Citing "circumstances beyond our control", the Syrian government abruptly canceled Arab League Secretary-General Naril Elaraby's scheduled visit to Damascus. Elaraby's office confirmed that the visit had been indefinitely postponed.

At least 34 people were reported dead by Syrian activists in a tank assault on Homs that also involved about 20 truckloads of soldiers armed with live ammunition. Two more were reportedly killed in Sarmin, while one was killed in Hama. State-run media claimed two Baath Party officials were abducted by "terrorists" near Al-Rastan. Activists and locals reported that heavy machine-gun fire was heard in the Bab Dreib and Bostan Diwan neighbourhoods of Homs in the evening after at least 2,000 protesters marched toward the area from the Bab Tadmor district. Activists claimed the city was facing an especially vigorous assault due to a recent spate of defections, with one activist saying about 40 soldiers in Homs defected after refusing to fire on protesters.

8 September

Military vehicles rolled into the village of Ibleen just after dawn in pursuit of defected soldiers, between three and five of whom were killed in the raid, according to a resident. Another resident told international media that five children under the age of 10 were among roughly a dozen villagers detained by troops in Ibleen. SANA reported that six security officers were killed and three more wounded in the operation, which it characterised as a raid to target "armed terrorist groups" and seize stockpiles of weapons.

In Homs, the army reportedly pelted the city with a heavy artillery barrage. Activists said areas where soldiers had been known to have defected were being targeted. At least 23 people were killed, residents told international media.

The Syrian opposition plan new mass Friday demonstrations, this time under the banner of "Friday of International Protection", referring to their campaign to get UN observers to monitor violence inside Syria, as a way to pressure the Syrian government.

9 September – "Friday of International Protection"

Syrians protested across the country, calling for international help to stop the crackdown. Large protests called "Friday for International Protection" were reported in cities including Qamishli in the northeast, Homs and Hama in the center of the country, and Deir ez-Zor in the east. "A 15-year-old boy was martyred when soldiers manning a checkpoint opened fire in the village of al-Rama, in Jabal al-Zawiyah," in the northwest, the Syrian Observatory for Human Rights said in a statement. The LCC said the boy was killed after he was injured with his brother by "random shooting" in the village. In Damascus, activists alleged 8 soldiers were executed after refusing to fire on unarmed demonstrators. At least 6 protesters were injured in Damascus, the LCC said.

The body of a defected soldier's 74-year-old brother, one of the people abducted by soldiers the previous morning in Ibleen, was returned to his family by the Syrian Army.

Altogether, 14 people were reported killed throughout Syria on 9 September.

10 September

Syrian police and soldiers allegedly killed 24 protesters, including at least 12 in Homs alone, as Nabil Elaraby, the head of the Arab League, met with Bashar al-Assad, urging him to stop violence and move forward with reforms. After the meeting, Elaraby announced that "a deal has been agreed to for reforms". The Syrian opposition were angered at Elaraby's meeting with Assad, arguing that "a deal for reform" is meaningless at this stage.

11 September

Troops surrounded several villages, including near the protest hubs of Deir ez-Zor and Deraa, and conducted house-to-house raids and arrests. Sawasiah, a Syrian human rights organisation, claimed that at least 113 civilians had been killed over the past seven days, including three who were apparently tortured to death in military prisons. Leaders of the Syrian opposition again met in Istanbul and were scheduled to speak with a Paris-based Syrian academic by phone to discuss the unification of anti-government factions into a more cohesive political force. Citing activists in Abu Kamal, the Syrian Observatory for Human Rights said a woman was killed at midday by a stray bullet fired by security forces conducting arrests in the eastern town. It also said its sources in Damascus had reported a teenager wounded by a bullet while attending a funeral that was attacked by security personnel the previous day died as a result of his injuries.

The body of Ghiyath Mattar, 26, was returned to his family in Daraya, a suburb of Damascus. Ghiyath played a key role in organizing antigovernment protests. A friend of Ghiyath who saw his upper body today said that there were bruises on the chest, and his face had traces of wounds. Security forces (most likely Air Force intelligence, according to friends and relatives) had detained Ghiyath on 6 September with another leading protest organizer in Daraya, Yahya Sharbaji.

12 September

Three prominent Syrian clerics of the Alawite sect, which President Bashar al-Assad belongs, have denounced the violence committed by the Syrian government against protesters. "We declare our innocence from these atrocities carried out by Bashar al-Assad and his aides who belong to all religious sects", Mohib Nisafi, Yassin Hussein and Mussa Mansour said in a joint statement from Homs. The three clerics denied state-media reports that members of the Shiite Alawite sect are being subjected to acts of killing and kidnapping in Homs, and said "The daily reports of kidnappings, killings and harassment of members of the Alawite sect are all untrue. They are designed and spread to cause divisions among people united against the regime".

Meanwhile, at least 26 civilians were killed in the Syrian government's ongoing crackdown on protesters, the Local Coordination Committees of Syria said. Among the dead was a 12-year-old boy shot to death when Syrian security forces fired on a funeral procession, according to the London-based Syrian Observatory for Human Rights.. The funeral procession was for a protester killed on 11 September, the observatory said. In addition, 17 people were killed during operations by the military and security forces in Hama as authorities searched for wanted activists and demonstrators, the organization said.

13 September

Protesters in Deraa and Homs burned the Russian flag in protest over Russia's threatened veto of a United Nations Security Council resolution condemning Assad.

14 September

Syrian rights activists say security forces have opened fire in northwestern villages Wednesday in an ongoing effort to crush dissent as the government rejected an Arab League demand for an end to the crackdown. Rights activists said government troops fired heavy machine guns during raids on several villages in Idlib province near the Turkish border. They say security forces cut local communications, blocked roads and made arrests.

The US ambassador Robert Stephen Ford and representatives from France, Germany, Canada, Japan, the Netherlands, the UK and the EU in an unprecedented gesture of solidarity with Syria's protest movement took part in a vigil for a prominent human rights activist Ghiyath Mattar believed to have been killed under torture by security forces.

15 September

A group of Syrian activists declared on Thursday a council representing a united front in opposition to al-Assad. About 140 figures, including exiled opponents and 70 dissidents inside Syria, were chosen as members of the new Syrian National Council, concluding a four-day meeting in the Turkish city of Istanbul. The council aims to help topple Assad within six months and form an interim government thereafter, Basma Kadmani, a Syrian exile living in France, announced.

Mass protests are planned for Friday, under the banner of Friday of "continuing until we bring down the regime"

16 September – "Friday of Continuing Until We Bring Down the Regime"