SAN SALVADOR, El Salvador (AP) _ A U.S. Army helicopter crashed into Lake Ilopango minutes after takeoff, killing the five U.S. military personnel on board, officials said.

The pilot of the UH-1H had reported mechanical trouble before it went down Monday morning just east of the capital of San Salvador, U.S. Embassy spokesman Jeff Brown said.

U.S. divers said they had located the spot where they believe the helicopter crashed but that the wreckage was about 270 feet down, too deep initially to reach.

The helicopter was based at Soto Cano air base 40 miles northeast of the Honduran capital of Tegucigalpa and took off from Salvadoran air force headquarters at Ilopango at 8:40 a.m., Brown said.

Embassy officials said the aircraft was on a ''routine inventory survey mission.''

Aboard were four Army crewmen who were based at Soto Cano and a U.S. Army administrative support specialist who was assigned to the U.S. military group in El Salvador, Brown said.

Names were withheld pending notification of relatives.

The military group consists of a maximum set by the U.S. Congress of 55 U.S. military personnel who train and advise the Salvadoran military.

Monday's fatal crash was the second of a Honduran-based American helicopter in El Salvador in less than two months.

On Jan. 2, leftist rebels battling the U.S.-backed government shot down a U.S. Army helicopter flying over eastern El Salvador. The pilot died in the crash. Guerrillas then shot and killed the two injured survivors.