Marines near the border fired the heaviest artillery barrage of the 10-day-old war with Iraq on Saturday, shelling Iraqi positions six miles inside occupied Kuwait.

Three Marines were reported killed in a vehicle accident related to the operation.Commanders at the 1st Marine Division headquarters said three batteries of 155mm howitzers fired on Iraqi positions near the L-shaped section of Kuwait's border with Saudi Arabia.

The Marines have moved up to the border and fired howitizers twice before, but a news-pool report from the scene said officers described Saturday's barrage as the biggest yet.

In the previous attacks, only one battery was fired. A battery normally consists of eight guns.

An Iraqi vehicle was reported destroyed in a brief firefight along the border during the Saturday operation.

A pool dispatch filed from divison headquarters said three Marines were killed and two injured in a related vehicle accident. It said at least one of the injured Marines was evacuated by helicopter.

Back behind the lines, it appeared the allied buildup was going slowly.

The U.S. military had already been behind schedule in getting new heavy divisions into position. In recent days the allies also decided to cut back on daytime convoys to the front - apparently wary that Iraq's largely untouched air force could spring a surprise attack on the long lines of vehicles.