North Korea said it reached an agreement with the US during talks this week on its nuclear programme, and the top US nuclear envoy expressed optimism on Friday that progress could be made when wider arms negotiations reconvene.

North Korea’s Foreign Ministry said three days of talks in Berlin between US envoy Christopher Hill and North Korea’s main nuclear negotiator Kim Kye Gwan had been held “in a positive and sincere atmosphere and a certain agreement was reached there.” No further details were given.

Hill said the talks laid the foundation for progress when six-nation nuclear negotiations resume and that he had agreed with his North Korean counterpart “on a number of issues.” He also declined to elaborate.

I am pretty convinced that we have the basis for a good session of the six-party talks,” Hill told reporters in Seoul after meeting South Korean Foreign Minister Song Min-soon and nuclear envoy Chun Yung-woo.

“I feel we do have a chance of making some progress at the next round, absolutely,” he said.

In Washington, the State Department offered a more muted assessment of the Berlin talks, saying no issues had been resolved. The talks involved an exchange of information designed to “prepare the way for real negotiations” once the six-nation negotiations resume, deputy spokesman Tom Casey said.

Hill and Kim met for three days and were believed to be discussing when to convene the next session of international talks on the North’s nuclear programs, among other issues. The last round in Beijing in December—held after the North conducted its first-ever nuclear test in October—ended without any breakthroughs.