WASHINGTON — Three detainees at Guantanamo Bay committed suicide in what apparently was a joint pact to protest the U.S. military prison that holds suspected terrorists, a senior administration official said Saturday. They are the first deaths reported at the detention center in Cuba, where the United States is holding about 460 men on suspicion of links to Al Qaeda and the Taliban.It was not immediately clear when the inmates died. It also was not clear whether the suicides were connected to a violent clash last month between detainees and military guards at Guantanamo. The Pentagon scheduled a briefing for later Saturday.