He said some 400,000 pounds (181 tonnes) of munitions, including anti-submarine depth charges, had been safely disposed of in an operation lasting several weeks.

"Imagine, that was just a portion!" he told reporters after witnessing the safe detonation of the remaining five tonnes from the cache at Crow Valley, a former gunnery range of US forces previously stationed at Clark Air Base. "This was really one of my first nightmares upon assuming office" in June last year.

Aquino said some of the bombs dated to 1947 and were previously stored at Caballo, a tiny island at the mouth of Manila Bay.

US forces handed over Clark, Subic Naval Base and several smaller facilities to Manila in 1992, a year after the Philippine senate refused to ratify a new bases treaty between the two allies. The two countries remain bound by a mutual defence treaty.

Manila asked Washington last year to help transport and dispose of the munitions because of the danger they posed while stored at Caballo, Aquino said.

"There (was) a possibility that there might be an unintended explosion that can detonate roughly about 400,000 pounds of explosives," he said.

The transfer of the bombs to Crow Valley was completed without any untoward incidents and their disposal was completed three weeks ahead of schedule, Aquino said.