U.S. experts have met with North Korean officials to discuss resuming stalled international talks about Pyongyang's nuclear program.
Former U.S. special envoy for North Korean policy Stephen Bosworth attended Wednesday's high level, but informal, meeting at a London hotel, but declined to discuss the talks.
Pyongyang withdrew from international talks on their nuclear program in 2009.
The meeting comes just hours after the United States and South Korea signed an agreement meant to provide greater deterrence against North Korea's nuclear weapons.
U.S. Defense Secretary Chuck Hagel and his South Korean counterpart Kim Kwan-jin signed the deal in Seoul during annual security talks.
Hagel said the plan underscores the countries' concern over the North's "nuclear and ballistic missile programs, its proliferation activities, and its chemical weapons."
"Today we signed a bilateral strategy for tailored deterrence against the threat of North Korean nuclear weapons and other weapons of mass destruction," Hagel said.
Few details were given on the expanded deterrence strategy, which comes after months of heightened tensions prompted by Pyongyang's third nuclear test in February.
North Korea's advancing nuclear weapons program has led to calls among some in South Korea for an extension of America's wartime control and command of South Korean forces. Seoul is scheduled to take over full command in 2015.
The two leaders did not make a decision on the matter, but agreed to review the timetable of the transfer while keeping an eye on the fluid security situation on the Korean peninsula.
North-South relations have only recently improved, with the two Koreas making limited progress on a series of cross-border business and humanitarian projects.