The United States on Wednesday added another 20 missing Americans as victims in Asia's tsunami disaster that has killed over 150,000 people.

"We have been able to confirm 16 Americans that died tragicallyin this natural disaster. We have also been able to, based on information we have gotten from eyewitnesses and other people on the scene, come to the conclusion that there are another 20 American citizens who we are now classifying as presumed dead," State Department deputy spokesman Adam Ereli said at a news briefing.

Of the 20 Americans, 19 were in Thailand and one was in Sri Lanka.

In addition, the United States is still seeking information onthe "welfare and whereabouts" of about 3,500 Americans in the region, Ereli said.

Ereli said that Washington is working with governments in the tsunami-hit region, nongovernmental organizations and people in the affected areas in a bid to track people down and verify their status.