BANDA ACEH, Indonesia – An American helicopter on a relief operation crashed in a rice paddy near Banda Aceh’s airport, injuring at least two American servicemen and causing the military to briefly suspend flights today, while strong aftershocks and security concerns provided more challenges for aid workers two weeks after the disaster hit.

The two men injured in the crash, along with eight other Navy personnel, were being flown back to their ship in the Lincoln battle group, said Captain Joe Plenzler, an American military spokesman in Medan, 250 miles southeast of Banda Aceh.

The SH60 helicopter crashed in a rice paddy about 500 yards from the airport in Banda Aceh, the main city on Indonesia’s tsunami-battered Sumatra Island, as it was trying to land, he said.

“There was no fireball but a little smoke. It landed on its side,” Captain Plenzler said, adding that the helicopter’s propeller was twisted from the impact.

American authorities said there was no indication the helicopter had been shot down. The American military suspended helicopter flights for about two hours after the crash.

The crash came a day after Indonesia warned aid workers that separatist rebels have taken shelter in camps for survivors and a burst of violence hit Sri Lanka, signaling a potential resurgence of long-simmering rebellions in both tsunami-hit countries that could hamper help for victims of the December 26 disaster.

Relief workers straining to help survivors of the earthquake and tsunami that has killed more than 150,000 people across 11 countries and left millions homeless and threatened by disease said they were being cautious but won’t let concerns about the rebellions slow the flow of aid.

“We don’t believe that aid workers are targets,” said the head of the U.N. relief effort in Indonesia’s troubled Aceh province, Joel Boutroue.

Aftershocks from the massive earthquake that spawned the killer waves, meanwhile, continued to rattle residents in the hardest-hit countries. A 6.2-magnitude temblor sent people scrambling from their homes early today in Banda Aceh, but no injuries or damage were reported.

The Indonesian government warning offered no details about the infiltration into survivor camps, but was issued hours after police in the provincial capital, Banda Aceh, blamed separatists for nighttime gunfire close to the main U.N. compound in town.

Local military spokesman Ahmad Yani Basuki told the state-run Antara news agency that volunteers must understand that Aceh “is not like other regions in Indonesia.”

“This is still a conflict-torn region,” he said. Indonesian authorities blamed separatist rebels for the shooting incident, near the house of a provincial police official. But the government routinely blames the rebels for violence – even without evidence.

“We were told by guards that it was probably one person shooting a few rounds and that was it,” Mr. Boutroue said.

The rebels have waged a separatist war in Aceh for nearly three decades in a conflict that has killed thousands. An unofficial truce settled in after the December 26 disaster, but recent skirmishes have prompted Indonesia’s military to step up patrols for the guerrillas.

Security concerns have also been heightened by the appearance of Laskar Mujahidin, an extremist group with alleged links to Al Qaeda. The group has set up an aid camp, but says it only wants to help and won’t target foreigners.

Still, the aid effort continued, with the World Food Program sending 170 staffers. Other agencies have similar numbers.

The American military, with hundreds of personnel on ships near Sumatra and in Sri Lanka, said aid workers must be on guard in restive areas.

“Security is a constant planning factor in all that we do,” American Army aid coordinator Major Nelson Chang said.

Refugee camps are being built on Sumatra to house and feed half a million homeless people. Bodies are still being pulled from the rubble and buried in mass graves.

Rain pounded relief workers yesterday, turning Banda Aceh airport – the hub for aid supplies – into a muddy mess and soaking piles of cardboard boxes of supplies sitting on the tarmac. Scores of tents where aid workers and soldiers camped became a quagmire.

Despite the troubles, a World Food Program spokesman, Mike Huggins, said help was getting to people in need.

“We are moving more food now than ever before and we’re getting it farther afield,” he said. Aid officials said they may have to feed as many as 2 million survivors a day for six months.

Australia and Germany, among other countries, have led the way in pledging nearly $4 billion in aid – the biggest relief package ever. President Bush called America’s $350 million only an “initial commitment” and essentially a line of credit that can be spent as aid officials identify needs.

Unicef chief Carol Bellamy, speaking on CBS’s “Face the Nation,” continued warning about the fate of children.

“There has been in the past in this region, even before this horrible tragedy, criminal trafficking syndicates, trafficking young people, children, largely for sex purposes. There has been one case so far identified in Indonesia: people have been taken into custody by the government police authorities,” she said, adding that most talk of child abuse and abduction so far are “rumors” about what “could happen.”

Also yesterday, a videotape shot as a tsunami swept through Aceh province aired for the first time and showed a roiling torrent of dark brown water engulfing a busy street, picking up cars and minivans and sending people scrambling up the sides of buildings.

The videotape, broadcast by Metro TV, was filmed by a cameraman named Hasyim who normally shoots weddings. He captured a horrific record of the unfolding disaster, starting minutes after a giant undersea earthquake in the Indian Ocean toppled buildings and including a scene hours later showing a long line of corpses covered with cloth.

The recording starts with people milling on the streets of the provincial capital, Banda Aceh, shortly after the world’s biggest quake in four decades – and climbing onto piles of rubble, unaware that a massive sea surge was heading toward them.

Some buildings had crumpled, with floors lying on top of one another, while others appeared undamaged.

As his videotape showed a building that became a pile of twisted girders, Hasyim told Metro TV that five construction workers were sleeping inside the unfinished structure when it collapsed, probably killing them all.