Updated

Two U.S. Navy construction troops and a Philippines marine were killed Tuesday in a roadside blast in the southern Philippines that officials said was likely an attack by suspected Al Qaeda-linked militants.

It was believed to be just the second time U.S. soldiers have been killed in the southern Philippines in violence blamed on the Abu Sayyaf group since American counterterrorism troops were deployed to the region in 2002, and the first fatalities in seven years.

One Philippine marine also was killed and two others were wounded in the blast on Jolo island, a poor, predominantly Muslim region where the Americans have been providing combat training and weapons to Filipino troops battling the Abu Sayyaf.

Philippine officials described the blast as being caused by a land mine, a description normally used for military-grade weapons. The U.S. Embassy said it was an improvised explosive device.

Military spokesman Lt. Col. Romeo Brawner said a Philippine military convoy joined by U.S. troops was on its way to Kagay village in Jolo's Indanan township where troops were building two school buildings and digging artesian wells when the land mine exploded.

One U.S. soldier died at the scene, while another who was critically wounded in the blast died a short time later, Brawner told The Associated Press.

They were from the Naval Construction Battalions, or Seabees, which gather skilled craftsmen like electricians and carpenters into special military units.

"They were not in combat," Brawner said. "These U.S. soldiers were there in the area to supervise the developmental projects in Indanan."

In a statement, the U.S. Embassy said the deaths happened when the soldiers' vehicle struck an improvised explosive device at about 8:45 a.m. during a resupply mission for the school construction project.

The troops were not identified pending notification of next of kin.

The Philippine government offered its condolences to the families of the slain soldiers and praised them for helping undertake civic projects and secure peace on Jolo, about 590 miles south of Manila, the capital.

Brawner said no suspects were immediately identified, but suspicion immediately fell on the well-armed Abu Sayyaf, which is blamed for numerous bombings, beheadings and kidnappings of Filipinos and foreigners in the south in recent years.

Maj. Gen. Benjamin Dolorfino, a military commander overseeing counterterrorism campaigns in the south, told The Associated Press that Abu Sayyaf had likely planted the explosive in Indanan, where the militants have jungle strongholds.

The U.S. Seabees were immediately pulled back from the school project in Indanan after the attack, Dolorfino said.

He said U.S troops have long been targets for militants in the south, and Tuesday's blast would not likely cause any change in Washington's resolve to keep troops there.

Two weeks ago, a suspected Abu Sayyaf militant or sympathizer hurled a grenade near U.S. troops unloading supplies at Jolo's pier. The Americans were not hurt, he said.

Abu Sayyaf attempts to sabotage U.S. projects indicated the militants were wary of losing community support, he said.

"They know that once education sets in, the villagers will be well-informed and hard to fool and to recruit," Dolorfino said.

Abu Sayyaf is believed to have about 400 fighters, to have received funds from Al Qaeda and is suspected of sheltering militants from the larger Southeast Asian terror group Jemaah Islamiyah.

An estimated 600 U.S. troops are currently stationed in the Philippines, mostly in the southern front lines of the Philippine military's operations against the Abu Sayyaf group and Jemaah Islamiyah.

In October 2002, a U.S. Green Beret was killed along with two Filipinos when a bomb loaded with nails exploded outside a cafe in Zamboanga city.