Timeline: Key dates in Syria's civil war

2011

- 15-16 March: Demonstrations held in Damascus for "a Syria without tyranny". Authorities clamp down on rallies in Damascus and Daraa to its south, slamming an "armed rebellion of Salafist groups".

- 23 March: Some 100 people reportedly killed in a crackdown in Daraa, cradle of the uprising. Protests spread across Syria from April with calls for Assad's overthrow.

- 30 July: An army colonel who defected from the military announces the formation of the Free Syrian Army. At its birth, the FSA is mainly composed of army defectors. Later, civilian volunteers form the majority of its fighters.

- 18 August: US President Barack Obama urges Assad to quit. Western and Arab governments later impose sanctions.

- 4 October: China and Russia veto a UN resolution condemning the government crackdown on protests. Two more aborted resolutions follow in 2012.

2012

- 1 March: The Syrian army regains control of Baba Amr, a rebel bastion in the central city of Homs, after a month of shelling that a non-governmental organisation says killed hundreds, including journalists Marie Colvin and Remi Ochlik.

- 30 June: Major powers reach an agreement in Geneva on a political transition that does not spell out Assad's future. The accord is never implemented.

- 18 July: Bombing in Damascus kills four top security officials, including Assad's brother-in-law Assef Shawkat. Two days later the FSA launches an offensive in which it seizes swaths of Aleppo, the main northern city.

The army hits back in August with heavy weapons, including warplanes.

- 11 November: Opposition groups sign a unity deal in Doha and form the Syrian National Coalition.

2013

- 14 February: Iran's Revolutionary Guards say a senior officer has been killed by Syrian rebels, having previously acknowledged some of its military "advisers" were inside Syria.

- 5 June: The Syrian army and fighters from the Lebanese Shiite movement Hezbollah recapture Qusayr, a strategic town near the Lebanese border.

Inter-confessional strife increases, pitting Shiite Muslims loyal to Assad's Alawite government against majority Sunni Muslims.

- 21 August: A sarin gas attack in the Damascus suburbs sparks international outrage. Hundreds are killed and in September, a Russian-US deal to dismantle Syria's chemical arsenal averts threatened US military action.

2014

- 3 January: Rebel groups launch an offensive against their erstwhile allies in the Islamic State of Iraq and the Levant, accusing the jihadist group of widespread abuses.

- 22 January: Talks begin in Geneva between Syrian government and opposition delegates at the behest of US and Russia, but end without a breakthrough.

UN mediator Lakhdar Brahimi indefinitely adjourns them on 15 February.

- 9 May: The Syrian army enters Homs's Old City neighbourhood, which has been under siege for nearly two years, after 2,000 rebel fighters withdraw under an unprecedented agreement with the government.

- 22 May: Government forces break a year-long siege of the central prison in Aleppo, cutting off a major rebel supply route.

- 22 May: Russia-China veto UN resolution to refer Syria to the International Criminal Court.

- 23 May: At least 44 people, including seven children and eight women were killed in air and ground operations across Syria, mounted by Assad forces, opposition activists say.

- 23 May: Both Assad forces and opposition rebels claim to have control over the northern city of Aleppo's prison after nearly two years of battle over it.

-24 May: At least 34 people were killed in air and ground operations across Syria carried out by Assad forces, opposition activists claim.

- 25 May: At least 37 people were killed in air and ground operations across Syria, allegedly mounted by Assad forces, opposition activists say. Hezbollah militants and Assad forces also claimed dead after opposition forces reportedly blew up a Syrian building in Aleppo.

- 26 May: The Jordanian Foreign Ministry deemed Syrian ambassador in Amman Bahjat Suleiman persona non grata, giving him 24 hours to leave the kingdom.

-26 May: In response to Jordan's move to expel its ambassador in Amman, Syria declared Jordan's charge d'affaires in Damascus "persona non grata".

-27 May: At least 70 people were killed in air and ground operations across Syria carried out by Assad forces, opposition activists claim.

-27 May: Operations allegedly by Assad's forces kill at least 22, including six children.

-28 May: Syrian military attacks killed 71 people in capital Damascus, Hama, Homs, Daraa, Deir ez-Zor, Idlib and Latakia.

- 29 May: Islamic State of Iraq and the Levant (ISIL) militants killed at least 21 people in clashes with armed groups linked to the Kurdish Democratic Union Party (PYD) in northeastern Syrian province of Al-Hasakah, the Kurdish party's leader said.

- 30 May: Operations allegedly by Assad's forces kill at least 48, including three children.

- 31 May: 71 people, including eight children and seven women, were killed in air and ground operations across Syria carried out by Assad's forces, according to opposition activists.