"We have tested 67 nuclear devices between the late 1940s and the late 1950s," Yun told a meeting at the Heritage Foundation.
"Radiation, I believe, is still there. Damages, I believe, are still there. And I believe there are lingering health effects too. I also believe we have a legal responsibility as well for what we did."
US compensation for the health problems and environmental damage caused by nuclear tests are currently being negotiated as part of the current compact talks with the Marshall Islands, Yun noted.
"That is part of the compact package that we have discussed with the Marshall Islands," he said.
The US has so far committed to providing $7.1 billion in compensation over a 20-year span to the Marshall Islands and two additional Pacific Island nations.