A car bomb damaged a U.S. military social center in a Brussels suburb today, slightly injuring an American guard, officials said. The attack was claimed by the same mysterious leftist group that bombed several other NATO-related targets in Belgium during the past three months.

The attack apparently signals an escalation in the bombing campaign waged by the group, which calls itself the Communist Combatant Cells. In a letter to Belgian newspapers, the group said that the blast was the first attack "able to wound or kill Yankee soldiers."

Previous attacks by the group caused no injuries, but the letter warned that the group believes human life is not "sacred."

The bombing took place about 3:30 a.m., according to a U.S. Army spokesman. Two U.S. military policemen stationed inside the building saw a car drive up to the entrance and two people get out and run away. The guards went outside to search the area and saw the two people get into a waiting car and drive away, the spokesman said. Shortly afterward, the car bomb exploded.

The guards escaped serious injury because they were not near the car when it exploded, the spokesman said. One of the guards was treated on the scene for cuts and went back to duty immediately.

The blast blew out windows and damaged walls and ceilings in the three-story building, the spokesman said. He estimated the extent of the damage at $500,000.

The building, which is used by U.S. military personnel in Brussels, houses a theater, chapel, snack bar, library and administrative offices.

The attack was the first time the group used a car bomb in what it has called its "war against NATO and military imperialism." Previously, the group left explosives near or on its targets, which have included the offices of U.S. defense contractors and political parties that are part of the coalition government of Belgian Prime Minister Wilfried Martens. A one-day series of coordinated bombings by the group last month forced NATO to shut down temporarily part of its emergency fuel pipeline in Belgium.

Belgian authorities investigating the bombings have made no arrests and apparently little progress in identifying the origins of the group. Several Belgian newspapers have reported that Belgian police have conferred with their counterparts in nearby countries to investigate possible links to terrorist groups in those nations.

In its communique today, the group said the bombing was dedicated to the West German terrorist group, the Red Army Faction.