MANILA, Philippines - Two bomb attacks in one day in the southern Philippines -- the first of which killed two U.S. soldiers -- could signal that al Qaeda-linked militants are launching a new offensive in the region, officials said Wednesday.

Military officials blamed the Abu Sayyaf group for planting explosives that damaged a bridge used by army tanks Tuesday night, just hours after an improvised land mine exploded under a military convoy carrying American troops.

Both attacks were in Indanan township on Jolo island, where the Abu Sayyaf has jungle strongholds and has evaded joint Philippine and U.S. military operations for years.

The attack on the convoy killed U.S. troops in the southern Philippines for the first time in seven years, and the bridge attack appeared to be directed at hampering the military's ability to respond to further attacks, said regional military commander Maj. Gen. Benjamin Dolorfino.

"One indication is they might be planning to attack military camps or detachments and they want to limit our mobility," Dolorfino told The Associated Press.

U.S. Maj. Bradley Gordon said the two Americans killed Tuesday were U.S. Army soldiers who were members of the task force deployed to help quell militants in the southern Philippines.

Dolorfino said the two Americans were in the front of a Humvee -- one was driving -- when it ran over a powerful improvised explosive device buried in the road. The blast was powerful enough to flip the vehicle over. One Philippines marine was also killed and two wounded.

Security analyst Zachary Abuza, who has made extensive studies on the Abu Sayyaf, said U.S. deaths were not likely to alter Washington's commitment of troops to the southern Philippines because the effort has been held up as a successful civic-oriented campaign that could be replicated elsewhere.

Filipino Sen. Miriam Defensor Santiago, however, questioned why the American troops were in a combat zone when they were supposed to be banned by the Philippine constitution from engaging in local combat.

Santiago has spearheaded efforts to get the government to scrap an agreement that allows American troops to stay in the south to provide training and other noncombat support to Filipino soldiers battling the Abu Sayyaf.

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 south to help the Philippines fight the Abu Sayyaf and Jemaah Islamiyah.