BARCELONA, DEC. 27 (SUNDAY) -- A U.S. Navy sailor died early today from injuries suffered when a youth tossed two grenades into a waterfront USO club, injuring five other sailors, authorities said.

The attack last night was the second in Barcelona directed at Americans in less than three months. A Catalonian separatist group claimed responsibility for the earlier attack, which injured eight persons at the U.S. consulate.

No group immediately claimed responsibility for yesterday's blast.

Witnesses told police a young man lobbed two grenades into the Iruna bar at about 6 p.m. (noon EST) while a group of U.S. sailors was inside. Part of the bar is rented by the USO as a reception center and club for sailors when U.S. Navy ships are in port, a spokesman for the city said.

In Washington, a Pentagon spokesman in Washington said officials did not know who was responsible for the attack.

Ronald Strong, 22, died early today from abdominal injuries, a spokeswoman at the Hospital del Mar in Barcelona said. Strong's rank and hometown were not given.

Four of the injured soldiers were being treated for minor injuries at local hospitals, and one was treated and returned to his ship, officials said.

State Department spokesman Ben Justesen said the sailors were from the USS Thorn and the frigate USS Donald B. Beary, which Spanish officials said arrived in Barcelona Friday. He said shore leave for sailors on both ships had been canceled.

The force of the blast shattered the waterfront bar's windows, ripped out a water pipe and damaged a car parked nearby.

The bar is a popular drinking spot for sailors on shore leave in this Mediterranean port city, 400 miles northeast of Madrid.