An extremist Islamic group with alleged Al Qaeda (search) links has set up a relief camp on Indonesia's tsunami-stricken Sumatra island, raising concerns it could stir up sentiment against U.S. and Australian troops helping distribute aid.

The Laskar Mujahidin (search) group posted a sign at its camp that read — in English — "Islamic Law Enforcement." Its members said Thursday they have been collecting corpses, distributing food and providing Islamic teaching for refugees here in predominantly Muslim Aceh province.

The presence of the extremist group, known for killing Christians in a sectarian conflict elsewhere in Indonesia (search), has generated fears that U.S. military personnel and others doing relief work could become terror targets.

It also underscores the fine line that foreigners, especially the U.S. military, must tread between being welcomed as Samaritans or viewed as invaders in a country where suspicion of outsiders runs deep.

U.S., Australian and South Korean government officials said they were aware of security threats and were taking precautions. One major aid agency said its staff had been ordered not to fly in U.S. helicopters.

Analysts said Islamic terrorists known to operate in Indonesia would be foolish to try to attack anyone helping the hundreds of thousands of tsunami victims, because it could result in aid groups pulling out and sour the militants' chances of building popular support.

But they warned that radical groups helping the relief effort would also try to stoke anti-Western sentiment — and wait for an opportunity to attack if public support for outside help wanes.

Ship-based U.S. Navy and Marine helicopter crews have flown scores of missions to coastal villages in recent days, delivering food and water and sometimes bringing injured survivors to the airport in Aceh's provincial capital, Banda Aceh. The Americans have been welcomed with gratitude.

A U.S. official in Aceh said on condition of anonymity that U.S. forces were aware of Laskar Mujahidin's presence.

"You've got to be on your toes," the official said. "We're watching them. Something can happen."

Lt. Cmdr. John Daniel, a spokesman for the USS Abraham Lincoln aircraft carrier battle group, said chopper crews were not taking special security precautions and that Indonesia's military — which has long fought separatist rebels in Aceh — was helping with security.

"We feel safe with the Indonesian military there," Daniel said. "We are cautious, but we're not doing anything special."

Australia's Foreign Minister Alexander Downer said his government had examined the potential terror threat and there was no cause for alarm. "We monitored this but we have no evidence of it being a problem," Downer said.

Indonesia, the world's most populous Muslim country, is predominantly moderate but hosts dozens of radical Islamic groups. Non-governmental organizations of all kinds — religious, political and others — have rushed to Sumatra to help in the relief effort, many ferried in on Indonesian military planes.

Among those brought in on military aircraft were 50 members of Laskar Mujahidin, according to Jundi, a member of the group. Like many Indonesians, he uses one name.

Jundi said Laskar Mujahidin has set up four posts in Aceh and has sent more than 200 members to Banda Aceh, where they have joined other aid organizations at a camp near the military airport.

The militant group was founded in the late 1990s to attacks priests and churches in eastern Indonesia's Maluku islands, which have pockets of Christians. Sectarian violence there left about 9,000 dead in 1999-2001.

The guerrillas worked in small bands, were often described as Ninjas, and reportedly wore masks when fighting. The organization's fighters numbered about 500 at its height in mid-2000.

The group, from Indonesia's main island of Java, is unlikely to attract much support among native Acehnese — a fiercely independent people. Three years ago, residents drove out another radical Islamic group, Laskar Jihad, which tried to open branches in the province.

Laskar Mujahidin has been accused of having links to foreign-based terrorist groups including Al Qaeda, according to a report by Sidney Jones, an expert on Indonesia's Islamic radical groups. It also reportedly accepted aid offered by an emissary of Usama bin Laden, Jones wrote.

In a speech Thursday in Singapore, Jones said Laskar Mujahidin's motives on Sumatra may have to do with fears that the foreign humanitarian effort was a veiled attempt to convert Muslims to Christianity.

Jundi said the group would not interfere with foreign troops — as long as they kept strictly to humanitarian operations.

"We are here to help our Muslim brothers," he said. "As long as they are here to help, we will have no problem with them."

But their presence highlighted the persistent danger of terrorism in Indonesia, and militant groups' murky, overlapping links.

Laskar Mujahidin was once headed by Abu Bakar Bashir, an Islamic cleric now on trial as an alleged leader of Jemaah Islamiyah, which has close Al Qaeda links. Some Jemaah Islamiyah members helped the Sept. 11 hijackers.

Jemaah Islamiyah is blamed for the 2002 Bali nightclub bombings that killed 202 people, a 2003 blast that killed 12 at Jakarta's J.W. Marriott hotel, and a car bombing outside the Australian Embassy two months ago that killed 10. Bashir denies being a terrorist and says Jemaah Islamiyah does not exist. During a court hearing last week, he offered prayers for the tsunami victims.

Indonesian police said the threat was exaggerated — a position Indonesian officials frequently took on Islamic terror groups before the Bali attack.

"This group is here for humanitarian reasons," said Indonesia's chief detective, Lt. Gen. Suyitno Landung. "We should not be prejudiced against them. I'm worried the media is exaggerating the threat of this group."

Against such a backdrop, the South Korean government issued a warning Thursday that it had "acquired intelligence that our relief groups in Indonesia and some other areas are becoming a possible target of terror attacks."

A South Korean Foreign Ministry official told the AP on condition of anonymity that the statement was "not based on verifiable intelligence" and was a "precautionary warning."

European governments and aid groups said they received no special terror warnings.

But Michel Brugiere, director of Medecins du Monde, or Doctors of the World, said that "given the context of the area where we are operating, we have very strict security measures in place."

"Our teams are told that they should not fly in American army helicopters, since we're concerned that they could be a particular target," Brugiere said.