The U.S. military — the largest group helping tsunami (search) survivors — will immediately start withdrawing troops from the relief efforts to feed and house more than 1 million refugees, the U.S. Pacific commander said Thursday.

Aid organizations responded to the announcement by Adm. Thomas Fargo (search) with disappointment but pledging to shoulder a greater share of the burden to aid tsunami survivors.

U.S. warships and helicopters "played a crucial role ... they're still playing that role," said Rob Holden, a member of a health assessment team from the United Nations (search), the U.S. military and other groups. "What we're trying to do ... is civilianize the humanitarian operations because we're aware that we won't have military assets forever."

Speaking in Kuala Lumpur, Malaysia, Fargo said the U.S. military "will start right now transferring functions to the appropriate host nations and international organizations."

Fargo noted that the humanitarian missions in Indonesia, India, Sri Lanka, Thailand and other countries affected by the Dec. 26 tsunami have moved from the "immediate relief phase ... toward rehabilitation and reconstruction."

The admiral suggested the withdrawal of the 15,000 American troops would be completed within 60 days, apparently meeting requests by Indonesian officials that foreign troops leave Aceh province on Sumatra island by the end of March.

Malaysian Defense Minister Najib Razak said Fargo told him the United States would scale down its Aceh relief operations by the end of February.

At a news conference, Fargo said the U.S. military would "respond to specific requests of host nations," adding that Washington "is committed to what clearly will be a long-term recovery effort."

About 1,000 Singaporean soldiers dispatched for relief efforts will begin pulling out Friday, a Singaporean military official said

Some aid groups had hoped the U.S. military would stay longer.

"The American military, the military hardware has been so useful," said Aine Fay, Indonesia director for the Irish aid group Concern. "I'm a bit taken aback that they're thinking of withdrawing it already."

Peter Biro, spokesman for the International Rescue Committee, said he'd like the U.S. military to remain.

"We're still in an emergency-type phase, there are so many gaps on the ground, we would like them to stay longer," he said.

"It seems like there still is a great need for airlifts and we know the Indonesian government has need of that," said Alissa Keny-Guyer, of the aid group Mercy Corps.

Some governments, meanwhile, expressed support and thanks Friday for the U.S. help.

"If they think it is the time to pull out they can do that, but they are always welcome and we are ready to accommodate them if they want to come back later," Thai govt spokesman Jakrapob Penkaire said of the U.S. military during a telephone interview with the AP.

The Sri Lankan government said Friday that it will not set a time frame for a U.S. departure.

"U.S. Marines are doing a fine job, specially in debris cleaning operations and this is highly appreciated," said Harim Peiris, the spokesman for President Chandrika Kumaratunga.

The withdrawal of foreign forces comes as the official death toll continues to climb. Almost four weeks after the disaster, reported deaths by government agencies in the affected countries range from nearly 158,000 to more than 221,000.

The U.S. Navy and Marines have delivered nearly 3.5 million pounds of aid supplies — about 150,000 pounds a day — since starting operations Jan. 1.

The U.N. World Food Program has distributed 5,600 tons of food to about 400,000 people in Aceh alone, said its Asia director, Tony Banbury. After visiting the obliterated coastal town of Meulaboh, Banbury said all tsunami survivors would be fed.

"We will get food aid to everyone who needs it," he said.

But worries over security in Aceh on the northern tip of Sumatra — where government forces and separatists rebels have fought for nearly three decades — threatened to complicate relief efforts.

Although the sides called a temporary cease-fire to facilitate the relief effort, a barrage of automatic gunfire was heard in the hills near the provincial capital, Banda Aceh, prompting residents of one refugee camp to run for cover.

It was unclear who fired the shots, but a local military commander acknowledged that an operation was under way in the area to counter rebel activity. No one was hurt, and the shooting did not appear to target refugees.

The Indonesian military had no comment on the incident. The state-run news agency quoted the army's chief of staff, Ryamizard Ryacudu, as saying the military had killed at least 120 rebels in the past two weeks.

In another incident, an Indonesian soldier in Aceh fired into the air during a U.S. aid delivery, narrowly missing the helicopter's rotor blades, witnesses said. The soldier apparently was trying to control 25 refugees lunging for supplies.

"Every now and then, you hit a crazy LZ (landing zone)," said Petty Officer 2nd Class Derrick Smith, 22, of Wichita Falls, Texas, a SH-60 Seahawk crewman from the USS Shoup. "Sometimes you can't even land — you just push food out."

In Sri Lanka — where about 79,000 refugees now live in relief centers in the Tamil-dominated northeast — the U.N. refugee agency asked the government to also help resettle tens of thousands of people displaced by a 20-year civil war.

And at a U.N. conference in Kobe, Japan, wealthy nations pledged about $8 million for a network of detection buoys in the Indian Ocean to warn coastal residents of future tsunamis. The pledges are enough to cover costs for the first year.

Salvano Briceno, director of the U.N. International Strategy for Disaster Reduction, said a basic warning system could be operational within 18 months. Experts have said such a system could have saved thousands of lives Dec. 26.

A Pacific system already in place eventually could extend to the Mediterranean, Caribbean and other seas, U.S. officials say.