Hopes are fading that Pyongyang will attend a fourth round of talks on ending its nuclear weapons programs, following revelations about South Korean nuclear tests. This may give North Korea a new reason to postpone negotiations indefinitely.

Diplomats from Washington, Seoul and Tokyo came out of a strategy meeting Friday in Japan, saying it is important to hold a fourth round of talks with Pyongyang this month, as originally scheduled.

They stressed talks should not be delayed by South Korea's recent admissions that it conducted its own secret nuclear experiments. The International Atomic Energy Agency is investigating South Korea's research with uranium and plutonium, and will issue a report to the United Nations next week.

Seoul says the 1982 and 2000 experiments were for peaceful purposes only, and were quickly dismantled.

But this issue could derail six-nation negotiations on dismantling North Korea's nuclear programs.

Pyongyang has yet to firmly commit to the talks, and in recent weeks has cast doubt it will engage at all. This is a pattern North Korea has repeated since its nuclear weapons programs were revealed in October 2002.

Pyongyang has continually blamed U.S. demands that it verifiably dismantle its nuclear facilities for rendering the negotiating process useless.

But in the past few days, North Korea appears to have seized on the South's nuclear experiments as a possible reason to cancel talks, saying the tests could instead trigger a "nuclear arms race" on the Korean Peninsula.

Choi Jin-wook, a senior researcher at the Korea Institute of National Unification in Seoul, says Pyongyang knows South Korea is not actually trying to develop nuclear weapons, and this is a ploy.

"Actually, it is kind of pretext, you know, excuse, for North Korea not to participate in the six-party talks," he said. "They understand it's not a real issue, but they try to use it as a excuse."

The nuclear dispute began two years ago, when the United States said Pyongyang had a secret uranium-based weapons program. Since then, China has arranged three rounds of talks with North Korea, South Korea, Japan, Russia and the United States to resolve the issue, but no progress has been made.

Many analysts believe North Korea wants to postpone talks for several reasons. One is that delays give the North more time to make nuclear weapons from its former plutonium energy reactors. Pyongyang sees this as giving it a stronger bargaining position to get badly needed foreign aid.

Lee Dong-bok, a North Korea expert at Myongji University in Seoul, says Pyongyang is also stalling in hopes that, in a few months, there will be a new U.S. administration that is more accommodating.

"The controversy about the extraction of the small amount of uranium in the South of Korea, I think that is going to give North Korea enough excuse to delay the six-party talks, maybe until after the presidential election in the United States," said Lee Dong-bok.

James Lilley is a former ambassador to South Korea and a senior fellow at the American Enterprise Institute in Washington. He recently said Pyongyang would seize on any excuse, even the rumored death of the wife of the North Korean leader Kim Jong Il, to avoid talking.

"My own sense is they've got a game plan on dealing with the United States, and her death might give them a convenient excuse to go into mourning, if it's true, and then just postpone the whole thing until after the American elections," said ambassador Lilley.

Still, diplomats are not entirely writing off a fourth round. Although Chinese officials this week have hinted that talks might not be held this month, a senior Communist Party official went to Pyongyang Friday to urge North Korea to show up at the negotiating table.

The British government also is joining in efforts to keep the talks moving. A senior Foreign Office official was heading to Pyongyang on Friday to encourage the North Koreans to continue the negotiations. Then on Sunday, U.S. Assistant Secretary of State James Kelly will hold meetings with Chinese officials in Beijing.