Hundreds of Americans remain missing two days after a devastating tsunami (search) struck Asia, but the State Department says a large number have been located and are safe.

The State Department said Tuesday that 12 Americans had died, seven in Sri Lanka and five in Thailand.

Bush administration officials sought to allay concerns about the missing, saying it might simply be a matter of not getting in touch with U.S. authorities in Asia.

Still, the State Department deputy spokesman Adam Ereli told reporters, "I would not presume to tell you that the casualty figure we have today is final. We just don't know."

Responding to the disaster, the U.S. Agency for International Development (search) added $20 million to the already promised $15 million.

The announcement was made after director Anthony S. Natsios met with Secretary of State Colin Powell (search) and Deputy Secretary Richard Armitage.

Describing the $20 million as a "line of credit," Ereli said, "We have identified an additional $20 million that we will be working to make available" to countries struck by the worst natural disaster in four decades.

"This is in response to what we're seeing out there, what we understand the needs to be, what we think can be usefully used at the present time," Ereli said.

The new total of $35 million is bound to be increased, he said. "We know the needs will grow," Ereli said. "The clear message is that we are committed to helping."

He appealed to Americans to contribute, as well. "America and Americans have a long and proud history of private charitable donations, and I would expect this case to be no different," Ereli said.

On Wednesday, President Bush is to make a brief statement at his Texas ranch about the Asian disaster following a regularly scheduled National Security Council meeting during which he will be updated on relief and recovery efforts, said White House deputy press secretary Trent Duffy.

Duffy declined to say whether the United States was planning to pledge more aid.

"As we continue to get our hands around the size of the effort's needs, that will continue to be addressed and assessed," Duffy said. "Secretary Powell clearly said that this is just the beginning — this is all preliminary — and the first thing we need to do is get a good assessment of what's absolutely necessary."

The Pentagon said Tuesday that it is establishing a command center at Utapao, Thailand, to support the tsunami emergency relief effort and to serve as a staging base for U.S. military and rescue aircraft.

"The focus of the mission will be to prevent further loss of life and human suffering by expeditiously applying resources to the overall relief effort," the Pentagon said in a written statement. The command center will be operated mainly by Marines of the 3rd Marine Expeditionary Force.

In addition to Air Force C-130 cargo planes ferrying relief supplies to Thailand from Yokota air base in Japan, and Navy P-3 Orion surveillance aircraft operating in the vicinity of Thailand, the Navy also is dispatching the USS Abraham Lincoln carrier strike group and the USS Bonhomme Richard expeditionary strike group to the area.

Maj. Guillermo Canedo, a spokesman for U.S. Pacific Command in Hawaii, said in a telephone interview that the Lincoln strike group was headed for the South China Sea, off the coast of Thailand, and the Bonhomme Richard strike group was headed to the Bay of Bengal, off Sri Lanka.

Canedo said it was not yet decided whether any of the approximately 2,200 Marines aboard the ships of the Bonhomme Richard strike group would go ashore in Sri Lanka or elsewhere.

Also the Air Force will send KC-135 aerial refueling aircraft from Japan and Guam to provide assistance as directed, the Pentagon said.

Pre-stocked supplies of plastic sheltering, food and water bags are on their way to Indonesia from Dubai in the Persian Gulf.

Powell, appearing on a string of morning television talk shows, said the Bush administration would contribute large sums.

"The United States has given more aid in the last four years than any other nation or combination of nations in the world," Powell said.