Two US navy servicemen and one Filipino marine were killed on Tuesday in a landmine attack in a stronghold of Islamic militants in the southern Philippines,officials said.
Philippine army spokesman Lieutenant-Colonel Romeo Brawner said two other Filipino soldiers were wounded when the vehicle they were riding in struck an improvised landmine near Indanan town on the island of Jolo.
They were the first deaths since 2002 among US forces deployed in the southern Philippines. In that year, one soldier in a restaurant was killed by a bomb on a motorcycle parked outside.
"We're still investigating to determine who was behind the explosion," Brawner said, adding the latest attack happened near a Marine outpost.
Jolo is one of the strongholds of the Abu Sayyaf, the smallest but deadliest of the Islamist militant groups in the Philippines. It has links with al Qaeda and the regional group Jemaah Islamiah.
Brawner said the two US Seabees, members of the US Navy's construction battalion, were in a convoy of vehicles returning to base after inspecting humanitarian projects in the area when the landmine detonated.
"They were not on combat operations" Brawner said. "They were part of a US Navy construction unit. They were non-combatants helping poor Muslim communities on Jolo."
US troops are deployed in the Philippines under the Visiting Forces Agreement between the two countries. On Tuesday, the Philippine Senate sent a non-binding resolution to the government calling for its re-negotiation.
Senators led by Miriam Defensor-Santiago, a political ally of President Gloria Macapagal Arroyo, argued the agreement was a one-sided deal in favour of Washington.
The senators said that the VFA had not been beneficial to the Philippines because the United States failed to provided enough aid to modernise the country's military capabilities. It also did not guarantee the rights of Filipinos in criminal cases filed against US troops.
They also cited media reports that claimed US troops deployed in the southern Philippines had engaged in combat with Abu Sayyaf rebels in violation of the agreement, which only provides for training and logistical support to Filipino troops.
"Why are they there in that conflict area?" asked Santiago, referring to the troops killed on Tuesday. "They should only be in the military camps advising and helping train Philippine soldiers."
The US embassy in Manila issued a statement confirming the death of two servicemen, but withheld their identities pending notification of the next of kin.
"They lost their lives serving others, and we will always be grateful for their contributions to improve the quality of life on Jolo," US Ambassador Kristie Kenny said in a statement.