The Defense Department says a joint U.S.-North Korean program to recover the remains of American troops killed during the Korean War could be restarted if six-nation nuclear disarmament talks succeed.

In response to a letter sent by Democratic presidential candidate Bill Richardson, Eric Edelman, an undersecretary of defense, wrote, "We are hopeful we can make verifiable progress in the six-party talks, and, in that context, we are prepared to discuss resuming joint field activities" with North Korea.

The Pentagon letter, given to The Associated Press on Friday by Richardson's office, said a resumption of the program would have to deal with "issues related to the safety and the security of our teams." It said the Defense Department was prepared to return the teams when the talks with — and conditions in — North Korea permit.

The Pentagon had no immediate response to a request to confirm Edelman's letter.

A previous U.S.-North Korean project to recover remains in the North was stopped in 2005 after Washington said security arrangements for its workers were insufficient. The program had recovered remains believed to be from 220 soldiers.

Richardson, governor of New Mexico, said in his letter to the Pentagon that about 8,100 troops are still unaccounted for.

Richardson traveled to North Korea in April and brought back what officials described as the remains of six American soldiers. A frequent visitor to the North, Richardson has contacts with senior North Korean officials.

Under six-nation nuclear talks, North Korea shut down its main nuclear reactor in July. It has promised to disable the reactor by year's end in exchange for energy aid and political concessions from its negotiating counterparts — the United States, China, Japan, South Korea and Russia.

Richardson said in a statement that as nuclear talks show progress, "the time is right to restart the process of finding and identifying American soldiers who gave their lives during the Korean War."

The Korean War ended in a 1953 cease-fire that has never been replaced by a peace treaty, leaving the two Koreas technically still at war.