ZAMBOANGA CITY – (UPDATE 3) Two US Navy soldiers and a member of the Philippine Marines were killed while two others were injured when a landmine exploded near a Marine detachment between the villages of Kagay and Luamsaing in Indanan, Sulu, around 8:30 a.m. Tuesday, a military spokesman said.

"There is no suspect yet" in the attack, Lieutenant Colonel Romeo Brawner, Armed Forces spokesman, informed the Philippine Daily Inquirer by text as of Tuesday afternoon.

Sulu is the hotbed of the Abu Sayyaf and is also a known hiding place of Jemaah Islamiyah members.

The US soldiers were on board a US hummer vehicle when the explosion happened, Brawner told reporters in briefing in Manila.

“They were not in combat, again we would like to emphasize that they were not in combat and they were escorted and they were being secured by members of the Philippine Marines, these US soldiers were there in the area again to supervise the developmental projects that they have been doing or working on in the island of Sulu particularly in Indanan,” Brawner said.

He added that the two US soldiers were non-combatant members of the US Navy and were in the engineering unit of the US Navy and were in Sulu to supervise the construction of the 5-kilometer Cagay Road.

Brawner added that no bullets were exchanged and the incident was a roadside bombing.

The military spokesman said that the AFP did not have the names and ranks of the US servicemen.

Brawner said that they were still determining the other details of the incident and they have not identified any suspects behind the latest attack.

“We don’t want to speculate,” Brawner said.

Nevertheless, Brawner confirmed that Abu Sayyaf Group members were active in Indanan, Sulu and that the Moro Nationalistic Liberation Front (MNLF) has established camps in the area although it added that the military did not consider MNLF as “lawless elements.”

In a separate interview with the Inquirer, Brawner said no one has claimed responsibility for the attack and that the military and the police had no suspect as of Tuesday afternoon.

Sulu is a known lair of the Abu Sayyaf, which the military said, has been coddling operatives of the Jemaah Islamiyah.

US Embassy spokesperson Rebecca Thompson said, “We are still investigating the incident.”

Thompson declined to release more details of the incident, the second first major attack against US forces on Sulu in recent months.

A few weeks ago, an unidentified person hurled a grenade on US troops unloading supplies at the Jolo pier. Nobody was injured in the incident, which has become controversial because US soldiers fired their weapon on the suspected position of the attacker, which was allegedly near a mosque.

Temojen Tulawie, provincial coordinator of the Consortium of Bangsamoro Civil Society in Sulu, said he saw the bodies of the two US soldiers on a military truck.

“They were white and they wore their usual light brown uniform," Tulawie said by phone.

Tulawie said the US forces had come from Sitio Laum Saing.

“While returning back, they passed between the area of Kagay and Bato-bato and that's where the explosion occurred," Tulawie said.

Senior Superintendent Alibuddin Esmail, Sulu police chief, said a red alert has been raised all over the island in the wake of the attack.

"Although the situation is somehow normalized after the incident, we cannot still discount the possibility of another attack," Esmail said.

He said the police had no suspect as of Tuesday afternoon.

Tulawie said an emergency meeting among members and officials of various civil society groups in Sulu had been called.

He admitted the situation was worrisome.

"Because this is the first time a US soldier was killed in Sulu and in an area where there had just been a fresh fire fight,” he said.

Tulawie said the incident was also “a big slap on the Visiting Forces Agreement."

"[US forces] along with Philippine Armed Forces may launch offensive actions in the area although we still cannot determine who was behind the attack," he said.

Major General Ben Dolorfino, the Western Mindanao Command chief, said he would rather let the AFP headquarters release details of the landmine blast.

But he said that before the explosion, a 45-minute firefight between government forces and unidentified gunmen broke out in Barangay (Village) Bitanag in Panamao, Sulu.

“So far, there had been no reported casualty on our side," Dolorfino said.