Twelve days after a tsunami (search) devastated areas of Asia, the State Department is trying to find some 2,500 Americans who may have been in harm's way. It is still not clear how many of those people may be truly missing in the disaster that killed about 160,000 people.

"I don't know how long it will take us to work our way through the list," Maura Harty, assistant secretary of state for consular affairs, said Thursday. "What I can guarantee you is we will not stop until everything that is knowable is known to us."

Seventeen Americans are confirmed fatalities, and 18 are considered missing and presumed dead in Thailand or Sri Lanka, Deputy State Department spokesman Adam Ereli said.

To try to resolve the fate of Americans still not located, he said, "we are working flat out, 24 hours a day."

"The task is far from over," Ereli said. But he noted that at the beginning of the week the department was confronted with 6,000 inquiries about Americans who were not accounted for and that was now down to 2,500. Many names have been struck as duplicative, he said.

Information from eyewitnesses and others on the scene is used in cases where the State Department (search) presumes Americans are dead, Ereli said.

"In each of these cases there is a specific reason to believe that the individual was in harm's way at the time of the tsunami," Ereli said.

The Pentagon (search), meanwhile, expanded its contribution to recovery efforts. The Army sent several helicopters to distribute supplies and dispatched about 100 people from bases in South Korea and the United States to deal with a variety of medical and logistics needs.

The Army also is sending four mortuary affairs teams from Fort Lee, Va., to help recover human remains and identify victims. Engineering support teams from the Army will help plan reconstruction.

Marine Brig. Gen. Frank Panter, who is leading the military's relief operation, said Thursday that the efforts were moving from emergency response to recovery, with more focus on engineering jobs such as removing debris and providing clean water.

"Initially the devastation, the impact it would make on you, was just terrible. It was saddening," Panter told CBS from Colombo, Sri Lanka.

President Bush, who has pledged the United States would provide $350 million in assistance, has personally contributed $10,000 to the relief effort, White House press secretary Scott McClellan said Wednesday.

In a speech on legal issues in Collinsville, Ill., Bush praised the U.S. military for its "heroic work" and urged Americans to continue to open their wallets.

"The most important contribution a person can make is cash," Bush said. "There's huge generosity here in America."

Citing the privacy of families, Ereli declined to identify the Americans presumed dead by name or in any other way, except to say none was a U.S. official.

The State Department has declined to estimate how many Americans may have perished. Officials suggested many of those not yet found simply may have failed to get in touch.

Last Sunday, Secretary of State Colin Powell (search) said he did not expect a huge number of American casualties. Families "have just not been able to reach out to their loved ones or their loved one is not able to reach out to them," he said.

Other governments that have lost people in the disaster have provided casualty estimates and totals.

At least 60 Germans died — the highest official toll of foreigners so far — and an additional 1,000 remain missing. Sweden has reported 52 of its citizens were killed and 1,903 remain missing.