North Korea expressed optimism Thursday over talks this week with a U.S. delegation on its nuclear program, raising hopes of breaking the impasse that has deadlocked arms negotiations.

The nuclear talks have been mired since last year over what the North will include in a declaration of its nuclear programs. The communist nation missed a year-end deadline to complete the declaration, which it had agreed to provide to the other countries in the negotiations.

North Korea's Foreign Ministry said Thursday it had discussed technical matters with the Americans for moving forward on that and other agreements from the arms talks.

"The negotiations proceeded in a sincere and constructive manner and progress was made there," the ministry said in a statement after the Americans left Pyongyang.

The ministry gave no further details in the statement carried by the North's official Korean Central News Agency.

The U.S. delegation arrived in Seoul from the North after a three-day visit, but has not yet commented publicly on the trip.

The U.S. recently has stepped back from its push for a detailed declaration addressing the North's alleged secret uranium enrichment program and nuclear cooperation with Syria.

Now, the U.S. says it wants the North to simply acknowledge the concerns and set up a system to verify the country does not continue such activity in the future.