Leftist guerrillas from the Portuguese group FP-25 claimed responsibility for an unsuccessful mortar attack on North Atlantic Treaty Organization warships in the port of Lisbon. Police said three shells from what was believed to be a 60-millimeter mortar were fired at six warships but fell short. The ships, on a routine annual visit, included the U.S. frigate R.E. Byrd. A Portuguese navy spokesman said the attack appeared to be part of a series of recent strikes against NATO throughout Western Europe.