Two U.S. soldiers and one Filipino marine were killed today by a roadside bomb in the southern Philippines, in the first deadly attack on U.S. forces there in seven years, Reuters quoted officials as saying. The Pentagon said an investigation was under way into the blast on the Island of Jolo, a stronghold of Islamic militants, but that early indications pointed to the use of an improvised explosive device, or IED, detonated intentionally. "This is the first time at least in any recent history that I can recall that any particular device of this nature was used against U.S. forces," said Pentagon spokesman Bryan Whitman. The bomb, which also wounded two Filipino soldiers, detonated while the group was driving near Indanan town on Jolo. The Pentagon said the troops had been on a resupply mission for a school construction project.