Indonesia's military said Sunday it had reports that separatist rebels were infiltrating refugee camps in tsunami-stricken Aceh province and warned relief workers to take extra care, the state news agency Antara reported.
The report gave no details of the infiltrations. It came hours after police in the provincial capital, Banda Aceh, blamed the separatists for a burst of gunfire close to the main United Nations compound in the town.
"Volunteer workers have been called to exercise more caution and understand that Aceh is not like other regions in Indonesia. This is still a conflict-torn region," Antara quoted local military spokesman Ahmad Yani Basuki as saying.
The head of the United Nations relief operation in Banda Aceh, Joel Boutroue, speaking after the shooting, said he did not believe relief workers were targeted.
"I don't see at this stage any hampering of our movement," he said. "We were told by guards at the gate it was probably one person shooting a few rounds of ammunition and that was it."
But he added security already was tight.
Meanwhile in Sri Lanka, two hand grenades hurled in a rare clash between Christians and Hindus killed at least three people and injured 37 others in an eastern region where international aid workers are helping tsunami victims, police said. No relief workers were hurt, officials said.
Police say Christians were angry that Hindus had demolished a church and may have carried out the attack in retaliation.
The Free Aceh rebels have been fighting a low-level war against Indonesian troops for an independent homeland in Aceh for more than 20 years. They declared a unilateral cease-fire and the military said it would not target suspected rebels during the emergency, but clashes have broken out in recent days.
A tropical downpour lashed Banda Aceh airport Sunday, turning the major hub for aid supplies to stricken Aceh province into a muddy mess, and soaking piles of cardboard boxes of aid sitting on the tarmac.
There were no reports that the landing strip for supply planes had become too flooded for use, although the ground around the scores of tents where aid workers and soldiers camped had become a quagmire.
The regular heavy rainfall in Indonesia could further complicate a relief effort already hamstrung by damaged infrastructure such as roads and bridges shattered by the huge quake and tsunami it unleashed.
Boutroue said the deluge also compounded the misery of survivors forced to live in tents and underscored the need to quickly build more permanent shelters for them.
Of the aid distribution, he said: "We're confident that most communities have been reached. I cannot say that everybody has been reached."
The U.S. military acknowledged that aid workers must remain vigilant while working in restive areas.
"Security is a constant planning factor in all that we do," said U.S. army aid coordinator Maj. Nelson Chang.
The World Food Program is readying to feed up to 1 million survivors for six months in Indonesia and a further 750,000 in Sri Lanka, the group's executive director, James Morris, said Saturday in Jakarta.
The United Nations and local governments are coordinating the massive relief effort and militaries from around the world have pitched in with transport and logistics.
American Navy personnel and Marines flew into shattered regions of Aceh province in northern Sumatra while Australian and New Zealand troops worked in a 55-bed field hospital they set up Saturday in Banda Aceh, the Australian Defense Force said.
Australia also is sending a troop ship, HMAS Kanimbla, packed with aid and equipment, that is due to arrive midweek, a military spokesman said on condition of anonymity.
The ship's commander "has never seen it so loaded up," the spokesman said.
The Kanimbla, steaming toward Sumatra from Australia's northern port of Darwin, was carrying two Sea King helicopters, two large landing craft that can take tons of cargo ashore in places with no port facilities, medical supplies and staff and communications equipment.
It also had on board military engineers, trucks, bulldozers, four-wheel drive vehicles and construction supplies to help with the rebuilding effort.
News reports Sunday in Malaysia said it will send hundreds of teenagers who serve in a national service program to Indonesia to help in tsunami relief operations.
CBS News Correspondent Byron Pitts, in Banda Aceh, Indonesia, says there's
"Every day, the helicopters are finding the people quicker and quicker. Every day, we are getting better at this," says Lt. Comm. John Bernard.
About 13,000 U.S. servicemen are now in Indonesia and surrounding seas, along with 10 ships and more on the way, the U.S. Navy said Saturday. The U.S. military says it is incurring $5.6 million a day in operating costs.
The Washington Post reports that U.S. charities report they've raised $337 millioin so far for tsunami and quake relief efforts. The newspaper says some are calling that "the greatest outpouring of donations for a foreign disaster in American history."