CHRONOLOGY: U.S. involvement in Somalia

(Reuters) - A U.S. air strike on Somalia three days ago killed up to 10 al Qaeda-affiliated "terrorists", but three of the most wanted suspects survived, a senior U.S. official said on Thursday.

Following are some key dates in Washington's relations with Somalia in the past 15 years.

December 1992 - The United States sends 28,000 troops to Somalia at head of "Operation Restore Hope", a U.N. military effort to quell Somalia's wartime famine.

October 1993 - 18 U.S. Army Rangers are killed when Somali militias shoot down two military helicopters. The United States later suspects the Somalis were trained by al Qaeda, and the event is dramatized in the movie "Black Hawk Down".

March 1994 - The United States ends its mission in Somalia.

August 1998 - Truck bombs claimed by al Qaeda kill 224 people at the U.S. embassies in Kenya and Tanzania. Suspects include Somali citizens and the United States receives reports that al Qaeda members are in Somalia.

December 2002 - The United States sends 1,300 military personnel to establish a counterterrorism unit near Somalia. Based in Djibouti, the task force is designed to hunt for militant groups in six Horn of Africa countries, including Somalia. Commanders discuss sharing security technology with regional forces and training them in counterterrorism techniques.

Early 2006 - Somali warlords form an "Alliance for the Restoration of Peace and Counterterrorism" in Mogadishu. Experts on Somalia say the CIA is funding the group, whose members have been battling Islamic militias for control of the country.

June 2006 - Galvanizing popular support with anti-U.S. rallying cries, Islamic militants take over Mogadishu and rout warlords.

December 2006 - Islamists flee Mogadishu as a joint Ethiopian and Somali government force captures the capital. Diplomats say Washington gave tacit support -- plus surveillance and intelligence help -- to its ally Ethiopia.

January 2007 - U.S. aircraft strike the southern village of Hayo, in an attempt to take out an al Qaeda cell accused of bombing two U.S. embassies in 1998 and an Israeli-owned hotel in 2002. The United States later says that up to 10 "terrorists" are killed, but all three of the most wanted suspects survived.