BANDA ACEH, Indonesia - Foreign aid workers in Indonesia's tsunami-stricken Aceh province must take military escorts to areas facing insurgency violence, the government announced today, 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 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 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 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 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 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 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.