BEIRUT (Reuters) - Syria has accepted a U.N.-sponsored peace plan, international envoy Kofi Annan said on Tuesday, as troops loyal to President Bashar al-Assad raided rebel forces who have taken refuge across the border in Lebanon. The United States reacted skeptically to Annan's announcement, saying it would judge Assad's sincerity in agreeing to the peace plan by what he did and not by what he said, given his record of "over-promising and under-delivering. ...