The White House on Wednesday asked the Indonesian government to explain why it appears to be making it more difficult for aid workers and journalists to travel into some of the areas of the Aceh-province hardest-hit by the tsunami.

"We've seen the reports. ... We'll seek further clarification from Indonesia (search) 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."

Amid warnings from the Indonesian military that aid workers in parts of the tsunami-battered Aceh province (search) could be vulnerable to attack by separatist rebels who have been fighting for an independent state there for decades, the government ordered them to register with the government before traveling outside the provincial capital of Banda Aceh (search). Those who failed to do so could face expulsion, the government said. Foreigners had been banned from the area before the tsunami.

More than 100,000 people were killed in the area and tens of thousands have been left homeless or in need.

But the military offered no evidence to back its claims that rebels could rob aid convoys or use refugee camps as hideouts, leading critics to say that the authorities are really moving to reassert control over the rebellion-wracked area.

At the same time, the Indonesian government made clear that foreign troops would be out of the country by the end of March.

U.S. Marines were forced to agree to not carry weapons or set up a base camp on Indonesian soil and scaled back plans to send hundreds of troops ashore to build roads and clear rubble. Indonesia also declined to let fighter pilots from the USS Abraham Lincoln (search), in the region leading the U.S. military's relief effort, use its airspace for training missions. So the ship steamed out of Indonesian waters so that the carrier-based pilots could meet the requirement that they do not go longer than 14 days without flying.

The moves reflect the unease with which Indonesia has faced a massive aid operation that has brought foreign military forces onto its soil.

"We want to make sure there is rapid and immediate relief provided to all the affected persons," McClellan said. "It remains a priority for the United States as well as the international relief organizations in the area."