SEOUL (Reuters) -- North Korea's pursuit of a second path to nuclear weapons by enriching uranium is a problem likely to persist and Pyongyang needs to come clean about its intentions, a U.S. envoy for the reclusive state said on September 6.
North Korea, which has produced enough plutonium for an estimated six to eight bombs, said on September 4 it had made advances in uranium enrichment, a move analysts saw as a tactic to put pressure on regional powers after a month of conciliatory gestures.
"This is not the first we have heard of HEU [highly enriched uranium] and it may not be the last," Stephen Bosworth told reporters in Seoul, a day after having talks with South Korean officials.
"If we are going to deal as we wish with the denuclearisation of the Korean peninsula, this is an issue that will have to be clarified," said Bosworth, who has just visited Beijing and will next visit Tokyo to discuss stalled six-country diplomatic efforts on ending the North's nuclear arms program.
The U.S. has long suspected North Korea of trying to enrich uranium for weapons but proliferation experts said the North is nowhere near a full scale program, and it would take several years at least before it could reach that stage.
Bosworth said the enrichment was a concern and: "We have just begun to consider the question of what we might do in response."
Yonhap News reported later on September 6, citing un unnamed Korean government official, that the United States and South Korea agreed that a two-way approach of sanctions and dialogue for North Korea would continue.
A switch to uranium would alarm Western powers because it could be done away from the prying eyes of U.S. spy satellites, it may lead to enhanced cooperation with Iran and it could lure customer states keen to start their own nuclear arms program.
North Korea's broken economy was dealt a heavy blow by UN sanctions for its nuclear test in May that were aimed at cutting into its arms trade, which is a vital source of cash that brings it an estimated hundreds of millions of dollars a year.
North Korea last week sent a diplomatic mission China, which is the reclusive state's biggest benefactor and has the greatest influence on the enforcement of UN sanctions.
The North's KCNA news agency reported on September 6 that Chinese officials said diplomatic exchanges between the two countries would be maintained and cooperation would grow, following meetings with the North's delegation led by Deputy Foreign Minister Kim Yong-il.
Analysts said the North's moves to warm ties by freeing U.S. and South Korean citizens it held captive and trying to restore frozen business connections with the South were aimed at helping it bring cash to its depleted coffers.
But in a move that could raise tension with Seoul, fire officials said on six South Koreans were missing near the border with North Korea after a sudden rise in a river possibly due to water released from a dam in the North.