U.S. President Barack Obama said Monday North Korea's release of two detained Americans is no solution to a "core problem" between the two countries, and urged Pyongyang to demonstrate seriousness about giving up its nuclear program.

Obama made his remarks to reporters in Beijing, stressing that Director for National Intelligence James Clapper conducted no "high-level policy discussions" with North Korean officials when he visited the communist nation to win the release of the two U.S. citizens, according to a transcript provided by the White House.

"We have been consistent in saying that when and if North Korea becomes serious about denuclearization on the peninsula and is prepared to have a conversation around that topic, then the United States is going to be very open to try to arrive at a solution that over the long term could lead to greater prosperity and security for North Korea," Obama said. 

"Until that time, there's going to be a core problem between us," he said.

It takes more than "small gestures" like the release of the two -- Kenneth Bae and Matthew Todd Miller -- for the two countries to resolve "a broader fundamental conflict," he said, adding that the U.S. has so far not seen "serious engagement on the part of Pyongyang to deal with that problem."

Obama was in Beijing for a summit of Asia-Pacific nations and a state visit to Beijing.

Clapper's trip to the North raised hopes for a breakthrough in U.S.-North Korea ties. But Obama said the visit was focused on the detainee issue and "did not touch on some of the broader issues that have been the source of primary concern when it comes to North Korea, in particular, its development of nuclear capacity."

The North's decision to release the two Americans came amid international efforts to adopt a U.N. General Assembly resolution that calls for referring the totalitarian regime to the International Criminal Court (ICC) for human rights violations.

The release of the two could be part of efforts to tone down the resolution.

The decision could also be an olive branch aimed at restarting the stalled negotiations on its nuclear program. U.S. officials have cited the detention of American citizens as a big stumbling block to improved relations between the two countries.

Six-party denuclearization talks, which bring together the two Koreas, China, Japan, Russia and the U.S., have been stalled since late 2008. Pyongyang has called for unconditional resumption of the talks, but the U.S. has demanded the North first demonstrate its denuclearization commitment. (Yonhap)