BEIJING, Sept. 21 (Yonhap) -- The chief nuclear negotiators of South and North Korea on Wednesday began a second round of talks to discuss terms for resuming the long-stalled six-nation talks on ending the North's nuclear weapons programs, officials said.

During the talks, scheduled to last through Wednesday at a hotel in Beijing, Wi Sung-lac of South Korea and Ri Yong-ho of North Korea were expected to discuss what nuclear measures the North must take before the six-party talks can resume, said a senior Seoul diplomat involving the talks.

After a two-hour morning session and a lunch break, the two sides were scheduled to hold "open-ended" negotiations from 2:30 p.m. (local time), the diplomat said.

The diplomat said that Wi was also expected to demand North Korea stop its uranium enrichment program (UEP), which was revealed by the North last November and would give the country a new source of fission material to make atomic bombs, in addition to its widely known plutonium-based nuclear weapons program.

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

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

Wi and Ri met on the sidelines of a regional security forum in July, the first such contact in more than two years.

The July contact in Indonesia and a subsequent meeting between senior U.S. and North Korean officials have raised prospects for resuming the six-party talks, but no major progress has been made.

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."