Lee took the same flight as Wu Dawei, China's newly appointed vice foreign minister, who was returning home following his visit to Seoul Monday, officials said.

The two are expected to hold an in-flight meeting before they begin talks in earnest on arrival in Beijing, Yonhap news agency said.

Lee, who is scheduled to return home on Wednesday, also plans to visit Tokyo on Thursday and Friday this week and the United States and Russia next week.

Yonhap said he is expected to discuss ways to break the deadlock at the six-country talks on ending the nuclear stand-off.

North Korea on Monday ruled out new discussions with the United States, one of the six nations, and described President George W. Bush as an "imbecile" and a "tyrant" worse than Adolf Hitler.

It was responding to Bush's description last week of North Korean leader Kim Jong-Il as a tyrant

Despite the North's strong attack, the State Department said it believed it would attend the next six-party round scheduled before the end of September.

Aside from the United States and North Korea, the talks bring together South Korea, China, Japan and Russia.

The stand-off over the North's quest for nuclear weapons began in October 2002 when Washington accused it of operating a secret programme based on enriched uranium in breach of a 1994 accord on freezing its separate plutonium program.

Pyongyang has denied running the uranium-based program but has restarted its plutonium program.

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