U.S. forces came under fire from two civilian vehicles near a training area in northern Kuwait on Monday, officials said. No one was hurt.

It was the third case of gunfire involving American forces in Kuwait in less than a week. On Tuesday, two Kuwaitis ambushed Marines during training exercises, killing one and wounding a second. Marines killed the two attackers.

The Americans did not return fire in the latest incident, according to U.S. officials, who refused to provide details.

The shooting occurred at 7:50 a.m., according to a statement by the U.S. Embassy in Kuwait. The shots were fired from two unidentified civilian sports utility vehicles, it said.

The U.S. military and the Kuwaiti Defense and Interior ministries were investigating, the embassy statement said.

A military official at Camp Doha, where U.S. forces are stationed, confirmed the shooting and said nobody was hurt.

A Kuwaiti Defense Ministry spokesman could not be reached for comment. The Interior Ministry would not immediately comment.

Kuwait said 15 men have confessed to helping plan the Oct. 8 shooting.

A day after that shooting, U.S. army soldiers fired a shot at a vehicle overtaking their Humvee utility vehicle when, according to U.S. officials, an occupant pointed a gun at their vehicle. Officials later said occupants of the civilian vehicle claimed only to have been holding a cell phone. No one was hurt.

U.S. forces have been training in Kuwait since the end of the 1991 Gulf War.

Many Kuwaitis consider the United States the friend that liberated their country from Iraqi occupation in the 1991 Gulf War. But some Kuwaiti Muslim fundamentalists see the U.S. presence here as a source of corrupting influence.

Neighboring Saudi Arabia, meanwhile, expressed concerned that Al Qaeda members may be in Kuwait, Saudi Interior Minister Prince Nayef said.

``The presence of Al Qaeda members in Kuwait harms us and we had hoped that those people would put their country's interest before anything else,'' Prince Nayef told reporters late Sunday.