Foreign aid workers in Indonesia's tsunami-stricken Aceh province (search) must take military escorts to areas facing insurgency violence, the government announced Thursday, the latest in a series of security demands that also require U.S. and other foreign troops providing relief to leave the country by the end of March.

The government's moves — which include an order that aid workers declare their travel plans or face expulsion — highlight its sensitivities over foreign military involvement in a humanitarian effort and underscore its efforts to regain control of Aceh province, the scene of a decades-old conflict between separatist rebels and federal troops accused of human rights abuses.

The United Nations (search) expressed concern that the new demands could create bottlenecks in aid deliveries.

Indonesian military spokesman Col. Ahmad Yani Basuki said in a telephone interview that the army considers only the areas around the provincial capital Banda Aceh and the stricken coastal town of Meulaboh safe for foreigners.

"Other areas aside from that are potential trouble spots," he said. Anyone going to the troubled zones must take military escorts. But Basuki warned: "We don't have enough personnel to secure everyone."

The latest restrictions placed on the international presence came as the aircraft carrier leading the U.S. military's tsunami relief effort steamed out of Indonesian waters Wednesday after the government declined to let the ship's fighter pilots use its airspace for training missions. The USS Abraham Lincoln's (search) diversion was not expected to affect aid flights, however.

U.S. Marines have also scaled back their plans to send hundreds of troops ashore to build roads and clear rubble. The two sides reached a compromise in which the Americans agreed not to set up a base camp on Indonesia or carry weapons.

Instead, the Marines — some 2,000 of whom were diverted to tsunami relief from duty in Iraq — will keep a "minimal footprint" in the country, with most returning to ships at night, said Col. Tom Greenwood, commander of the 15th Marine Expeditionary Unit.

In Washington, the White House asked the Indonesian government to explain why it was demanding that the U.S. military and other foreign troops providing disaster relief leave the country by March 31.

"We've seen the reports. ... We'll seek further clarification from Indonesia about what this means," said Scott McClellan, press secretary to President Bush. "We hope that the government of Indonesia and the military in Indonesia will continue the strong support they have provided to the international relief efforts so far."

In announcing the decision, Indonesian Vice President Jusuf Kalla said Tuesday that "a three-month period is enough, even sooner the better."

Cabinet Secretary Sudi Silalahi explained that Indonesia (search) hopes to take over the humanitarian work by March 26, which will be exactly three months after the massive 9.0-magnitude earthquake set off waves across southern Asia and Africa, that killed more than 150,000 people, two-thirds of them on Sumatra.

Starting Jan. 26, Indonesia will "gradually take over the role of foreign military and nonmilitary assistance," Silalahi said. By Feb. 26, he said, Indonesia's role should be larger than that of the foreigners.

Indonesia — where the tsunami killed more than 106,000 people — is not the only affected country that is ambivalent about U.S. military aid.

After the earthquake and tsunami, the U.S. military dispatched the Abraham Lincoln battle group to Sumatra and three ships carrying Marines toward Sri Lanka, where more than 30,000 people were killed. But two ships carrying Marines were diverted to Sumatra after Sri Lanka downgraded its request for help. India, where more than 10,000 were killed, rebuffed U.S. aid offers.

Some 13,000 U.S. military personnel, most of them aboard ships in the Abraham Lincoln's battle group, are taking part in the relief effort.

In Indonesia, hundreds of troops from other nations are also helping out, along with U.N. agencies and scores of non-governmental aid groups.

Australia has more than 600 troops in Aceh and expects to have about 300 more by week's end. Japan has sent two ships with 350 troops, and has promised to deploy about 1,000. Germany and Britain each has a smaller presence, involving mostly medical teams.

They, too, have agreed not to carry weapons while on Indonesian soil and are leaving security to the Indonesian military.

Both government troops and separatist rebels in Aceh say they won't launch attacks during the tsunami emergency. Indonesian soldiers and witnesses have described at least one clash in detail to The Associated Press, involving rebels who were either seeking food or trying to visit relatives.

The Indonesian government has traditionally barred foreigners from visiting Aceh, relenting after the tsunami struck and no other option existed but to invite foreign troops to deliver aid and set up field hospitals.

Indonesian authorities are now moving reassert control. On Wednesday, they ordered aid workers to declare travel plans or face expulsion from Aceh, saying it was for their safety.

The statement from Indonesia's relief chief also said that if groups head to regions considered dangerous, "then their safety will be organized by the national security authority." It was not known if that meant aid organizations may get military escorts.

Australian Prime Minister John Howard described the demand as "a good idea."

But Australian National University defense expert Clive Williams said the Indonesians want to keep close tabs on foreigners to conceal corruption.

"The big problem with dealing with (the military) in Aceh is that they're involved in a lot of corruption there and the reason I think they don't want people to go to some areas is because they're involved in human rights abuses," Williams said.

U.N. officials worried the new rules might delay the delivery of supplies.

"Any requirements that would create any additional bottlenecks or delays or otherwise adversely affect our operations need to be reviewed very carefully," said Kevin Kennedy at the U.N. Office for the Coordination of Humanitarian Affairs.

The USS Abraham Lincoln's diversion to international waters did not interrupt the steady stream of helicopter flights delivering aid along the devastated coast of Sumatra island, because they were able to refuel on other Navy ships closer to shore, said Lt. Cmdr. John M. Daniels.

Under Navy rules, pilots of carrier-based warplanes cannot go longer than 14 days without flying, or their skills are considered to have degraded too far and they have to undergo extensive retraining.

The bulk of the Marines' mission, meanwhile, has become ferrying aid workers and transporting food from the amphibious assault ship USS Bonhomme Richard (search). On Wednesday, Marine helicopters flew the first mission to the shattered city of Calang to drop off a French medical team. Helicopters also delivered supplies to Indonesian troops in Meulaboh, farther south.

Capt. David Shealy swooped his helicopter down on a scene of utter destruction — palm trees lying strewn across a beach, their roots sticking out of the sand. Rice paddies were filled with mud. Houses had been turned into piles of rubble, or washed out to sea. Bridges were buckled and broken.

But as Shealy lowered his helicopter to hover just a few feet over a road, hundreds of people suddenly appeared, swarming around, arms outstretched.

"It's like nothing I've ever seen before," said Shealy, of Dillon, S.C.