The United States has suspended its efforts to recover the remains of missing US servicemen in North Korea.
Thousands of US troops went missing in what is now North Korea
A Pentagon spokesman said the restrictions placed on the US teams inside North Korea were too great to make recovery operations feasible.
The decision comes amid mounting tension over North Korea's nuclear ambitions.
The teams have been searching the reclusive state for the remains of Korean War casualties since 1996.
They have recovered hundreds of sets of remains, and North Korea has been paid millions of dollars.
But the North Koreans - who are sensitive to having foreigners on their soil for fear of espionage - have always strictly controlled the movements and communications of the American teams.
The US said on Wednesday that the conditions under which its recovery teams worked had become intolerable.
A US government official said the final straw was the refusal by the North Korean authorities to allow any kind of communication system operating between teams in different areas.
The official said this had become a safety issue for American personnel and the recovery operations had been suspended.
"North Korea has, over the last several weeks, created an atmosphere and an environment unconducive to the continued presence of American personnel in North Korea," said Lt Cmdr Jason Salata, a spokesman for US Pacific Command.
But a statement by the command said the co-operation would be resumed if an "appropriate environment" was created.
BBC Pentagon correspondent Adam Brookes says that these operations are one of only a tiny handful of official contacts between the US and North Korea.
Their suspension reflects the near-impossibility of co-operation between the two countries on even the simplest of tasks, he says.
The programme has been suspended once before
There are still about 8,000 US servicemen classed as missing in North Korea, and many of their remains are thought to be recoverable.