A timeline of this year's anti-government unrest in Yemen:

January 22: Hundreds of students and other protesters gather at Sana'a University, calling for an end to the 32-year rule of President Ali Abdullah Saleh. The demonstrators apparently were inspired by the protests that led to the ouster of Tunisia's president.

March 1: Tens of thousands of demonstrators demand the ouster of Mr. Saleh. He fires five of 22 provincial governors, some for criticizing a crackdown on the protests.

March 18: As protest crowds swell, security forces open fire in Sana'a, killing at least 52 people. President Saleh declares a state of emergency. World leaders criticize the crackdown.

March 20-21: President Saleh dismisses his entire Cabinet. Some senior military commanders join the protesters calling for the president's ouster.

April 2-3: Yemen's opposition leaders urge President Saleh to hand over power to Vice President Abed Rabbo Mansour Hadi. He refuses. Rival demonstrators clash throughout the country.

April 10-11: Gulf Cooperation Council ministers urge President Saleh to transfer his powers to his vice president. Mr. Saleh welcomes the proposal, but does not specify a timeline for stepping down.

April 21-25: The GCC presents President Saleh with a plan for ending the political impasse and unrest.

April 30-May 1: Yemen's main opposition coalition accuses President Saleh of refusing to sign the Gulf agreement. Mr. Saleh says he will sign as the leader of the ruling General People's Congress party but not in his capacity as president, as the plan requires.

May 21-22: Yemen's opposition says it has signed a Gulf-brokered deal that would see President Saleh's transfer of power within a month. Mr. Saleh denounces the proposed deal as a “coup.”

June 3: President Saleh is wounded during an attack on the presidential compound in Sana'a.

June 4: Mr. Saleh flies to Saudi Arabia for treatment of his injuries. Vice President Abed Rabbo Mansour Hadi takes over. Government forces and those loyal to tribal leader Sheikh Sadiq al-Ahmar accept a Saudi-brokered cease-fire.

July 17: Tens of thousands of people rally against the president on the 33rd anniversary of his rule. Fighting between government forces and Islamists in the southern town of Zinjibar reaches its fiercest level since May.

August 17: Anti-government activists elect a 143-member “national council” to explore ways of taking power from President Saleh.

September 12: Mr. Saleh authorizes his deputy to begin talks with the opposition and to sign off on a GCC plan to transfer power and form a national unity government. A GCC representative leaves Yemen with no word of a deal.

September 23: President Saleh returns to Yemen, calling for a truce and talks to end the political crisis.

November 23: President Saleh signs the GCC power transfer agreement at a ceremony in Saudi Arabia.