A timeline of Ali Abdullah Saleh's 33-year rule

July 1978 Saleh takes power in then North Yemen.

May 1990 Pro-Western North Yemen and socialist South Yemen merge after 300 years of separation to form a new republic.

October 2000 A US warship, the USS Cole, is attacked in Aden harbour by Al Qaeda bombers, killing 17 sailors.

November 2001 Saleh declares support for US President George W Bush's "war on terror".

February 2008 A fragile truce is signed with North Yemen's Houthis, a Zaidi Shiite tribe, but the four-year revolt soon resumes. Saleh unilaterally declares the war over in July 2008. Full-scale fighting resumes a year later.

January 2009 Al Qaeda's Yemeni and Saudi wings merge in a new group called Al Qaeda in the Arabian Peninsula (AQAP).

January 29, 2011 Saleh supporters attack and disperse Yemenis who try to march to the Egyptian embassy in Sanaa to express solidarity with Egyptian anti-government demonstrators.

March 2 The opposition presents Saleh with a plan for a smooth transition of power, offering him an exit route.

March 18 Snipers kill 52 protesters among crowds that flock to a sit-in at Sanaa University after Friday prayers. Saleh declares a state of emergency.

March 20 Saleh dismisses his government.

March 21 Senior army commanders, including Saleh ally General Ali Mohsen, commander of the northwest military zone, say they have switched support to pro-democracy activists.

March 23 Saleh offers to step down by the end of 2011. He also proposes holding a referendum on a new constitution followed by a parliamentary election and a presidential vote.

April 23 Saleh agrees to step down in weeks in return for immunity from prosecution. The opposition agrees to the plan.

April 25 The opposition agrees to take part in a transitional government under a Gulf-negotiated peace plan.

May 21 Yemen's opposition signs the transition deal.

May 22 Five members of the ruling party sign the deal, but Gulf Arab states suspend it after Saleh asks for additional conditions and diplomats fail to persuade him to sign it.

June 3 Shells strike Saleh's palace in Sanaa, killing seven people and wounding the president, the prime minister, his deputy and the parliament speaker. The attack is blamed by the government on tribesmen.

June 4 Saleh flies to Saudi Arabia for treatment after the attack on his palace. Vice president Hadi becomes acting president.

August 10 Saleh agrees to look at restarting a Gulf Arab initiative aimed at ending the violent political standoff.

August 16 Saleh says he will soon return home from Saudi and reiterates that he will only hand over power "via elections, not via coups".

September 23 Saleh returns from Saudi Arabia, greeted by gunfire and explosions.

October 21 The UN Security Council urges Saleh to sign a deal requiring him to step down in exchange for immunity.

November 23 Saleh signs a deal brokered by Gulf states in Saudi Arabia. Saleh hands over to his deputy, Mr Hadi, who forms a new government with the opposition.

January 22, 2012 Saleh apologises to Yemenis and leaves Yemen for Oman on his way to the United States for more treatment for his injuries.

January 28 Saleh leaves Oman for the United States and later says he will return home before the election.

February 21 Uncontested presidential election.