Following is a timeline of events in Syria since protests began:

March 15, 2011 - About 40 people join a protest in Old Damascus, chanting political slogans in a brief first challenge to the ruling Baath Party before dispersing into side streets.

March 18 - Security forces kill three protesters in southern Deraa, residents say. The demonstrators were demanding political freedoms and an end to corruption.

March 22 - Hundreds of people march in Deraa and Nawa demanding freedom in the fifth straight day of demonstrations challenging the government.

March 24 - President Bashar Assad orders the formation of a committee to raise living standards and study scrapping the emergency law in place in Syria for the last 48 years.

March 25 - At least 200 people march in Damascus and there are reports of at least 23 dead around the country including, for the first time, in Damascus.

March 29 - Government resigns. Assad appoints Naji al-Otari, head of the government that stepped down, as caretaker prime minister. Thousands of Syrians hold pro-government rallies.

April 19 - Government passes bill lifting emergency rule.

Sept. 15 - Syrian opposition activists announce a Syrian National Council to provide an alternative to government.

July 31 - Syrian tanks storm Hama, residents say, after a month-long siege. At least 80 people are killed.

Nov. 12 - Arab League suspends Syria.

Dec. 7 - Assad denies ordering troops to kill peaceful demonstrators, telling US television channel ABC only a "crazy" leader kills his own people.

Dec. 19 - Syria signs Arab League peace plan and agrees to let observers into the country to monitor the deal.

Dec. 23 - Twin suicide bombs target two security buildings in Damascus, killing 44 people. Syria says al-Qaeda terrorists while the opposition members blame the government.

Feb. 4 - Russia and China veto a resolution in UN Security Council, backed by Arab League, calling for Assad to step down. The UN General Assembly approves a resolution on Feb. 16 endorsing the Arab League plan calling for Assad to step aside.

Feb. 22 - More than 80 people are killed in Homs including two foreign journalists. Hundreds of people have now been killed in daily bombardments of the city by Assad's besieging forces.

Feb. 23 - Former UN Secretary-General Kofi Annan is appointed UN-Arab League envoy to Syria.

Feb. 24 - Foreign ministers from more than 50 countries meet in Tunis for the inaugural "Friends of Syria" meeting. Russia and China, allies of Syria, do not attend.

Feb. 28 - Assad decrees that a new constitution is in force after officials say nearly 90 percent of voters endorsed it in a Feb. 26 referendum. Opponents and the West dismiss it as a sham.

March 1 - Syrian rebels pull out of the besieged Baba Amr district of Homs after more than three weeks of bombardment.

March 9 - The United Nations estimates at least 30,000 refugees have fled Syria since the start of the conflict

March 11 - Annan ends talks with Assad and leaves Syria with little sign of progress. Assad tells Annan opposition "terrorists" are blocking any political solution.

March 27 - Syria accepts the UN-sponsored peace plan.

April 1 - At second "Friends of Syria" meeting, Western and Arab nations warn Assad not to delay adopting the peace plan.

April 12 - UN-backed ceasefire comes into effect. Four days later monitors start their mission in Syria to oversee the ceasefire which is undermined by persistent violence.

May 7 - Syria says voters turned out in large numbers for a parliamentary election it sees as central to a reform program. Opposition supporters denounce the exercise as a sham.

May 10 - Annan condemns attacks in Damascus in which two bomb explosions have killed 55 people and wounded 372 in the capital damaging an intelligence complex involved in Assad's crackdown. A week later UN Secretary-General Ban Ki-moon says he believes al Qaeda was responsible for the two bombs. He also says that at least 10,000 people have now been killed.

May 25 - At least 108 people are killed, including many children, in an artillery barrage on the Syrian town of Houla in one of the bloodiest days of the conflict.

May 27 - UN Security Council unanimously condemns the killings in Houla, confirmed by United Nations observers. Syria denies carrying out the massacre.

May 28 - Syrian activists say Assad's forces have killed at least 41 people, including eight children, in an artillery assault on the city of Hama.

Russian Foreign Minister Sergei Lavrov says that Moscow is alarmed by the deaths but that it was clear both Assad's government and rebels were to blame. Kofi Annan arrives in Syria and will hold talks with Assad in Syria on May 29.