BEIJING (Yonhap News) -- The nuclear envoys of South and North Korea met for three hours in Beijing on Wednesday but failed to agree on terms of re-starting stalled six-party talks on the North's nuclear programs, both sides said.

 Wi Sung-lac of South Korea and Ri Yong-ho of North Korea parted ways without agreement on whether they would meet again, but they said  their discussions were "useful."

 "We discussed the nuclear problem in general, and a meeting such as this is part of the efforts to restart the six-party talks," Wi told reporters after the meeting at the private Chang An Club in the center of Beijing. "We will keep putting in these efforts."

 Ri also spoke of "constructive and useful" dialogue he had with Wi, but reiterated a call for the resumption of the six-party talks with no strings attached.

"Based on the result of this meeting, we will work toward the quick resumption of the six-party talks without preconditions," Ri said.

According to South Korean officials, the sticking point was South Korea's demand for North Korea to take some preemptive measures to back up its denuclearization pledge before resuming the six-party talks.

Actions North Korea was advised to take included a halt to its uranium enrichment program (UEP), a re-entry of U.N. nuclear inspectors and a moratorium on missile and nuclear tests, they said.

While hedging the South Korean demands, North Korea insisted that the six-party forum should be re-opened without any conditions attached, according to South Korean officials.

"Our stance is that North Korea must go into the (six-party) negotiations after suspending the UEP," a South Korean diplomat said, speaking on the condition of anonymity.

Chances for progress appeared to be low as the North's chief envoy  on Monday repeated calls for an "unconditional" resumption of the six-party forum.

A high-ranking South Korean government official said the Beijing meeting wasn't entirely lost, adding he was hopeful that continued inter-Korean dialogue could help make progress on North Korea's denuclearization.

"Through this meeting, we did develop better understanding of each other in some areas, and cleared doubts and misunderstanding in others," the official said. "North Korea appeared to believe that we were opposed to holding the six-party talks, but that has been clarified."

The official said South Korea raised the issue of North Korea's two deadly provocations on the South last year. Seoul is demanding Pyongyang take responsibility for torpedoing the warship Cheonan and shelling the border island of Yeonpyeong. Both attacks claimed a total of 50 lives.

On Wednesday, the North "had no particular reaction" to the South's demand, the official said.

The Beijing meeting was the second of its kind since the first one held in Indonesia in July on the sidelines of an  Asian security forum. That led to a high-level contact between North Korea and the U.S. in New York a few weeks later.

It's unclear whether Wednesday's inter-Korean meeting in Beijing would set the stage for another high-level U.S.-North Korea contact.

The six-party talks grouping the two Koreas, the U.S., China, Japan and Russia have been dormant since Pyongyang quit in April

2009 and conducted its second nuclear test a month later.

The North's military attacks on South Korea last year, together with its self-confessed uranium enrichment program, have created new hurdles to efforts by regional powers to reopen the six-nation talks.

After sharply raising tensions, the North has expressed its willingness in recent months to return to the talks aimed at dismantling its nuclear program in exchange for economic assistance.

The question now is whether Pyongyang will accept "pre-steps"

demanded by Seoul and Washington before the resumption of the six-party talks.

Seoul and Washington have insisted that Pyongyang halt all nuclear activities, including its uranium enrichment program, and allow U.N. inspectors to monitor the suspension before the six-party talks reopen.

On Tuesday, Wi told reporters that he wants to achieve a "fruitful result" at the Wednesday meeting with an "open and flexible mind."