Russia has replaced its lead negotiator in six-party talks aimed at ending North Korea's nuclear weapons programme, the Russian Embassy in Beijing and the Chinese Foreign Ministry said on Sunday.

The new lead negotiator is Russia's ambassador to China, Sergey Razov, replacing Alexander Alexeyev, deputy foreign minister in charge of Asia.

An official at the Russian embassy declined to give a reason for the change.

Delegations are arriving in Beijing this weekend, and talks between the two Koreas, the United States, Japan, Russia and China resume in Beijing on Monday.

Razov, 53, has been ambassador to China since July 2005. A career diplomat, he has also served as ambassador to Mongolia and Poland and was a deputy minister of foreign affairs before his posting to Beijing.

Alexeyev had led the Russian delegation in the six-party talks on North Korea since August 2004. The 59-year-old career diplomat has a record of high-profile diplomatic posts, including ambassador to Pakistan and Russia's envoy to the Organisation for Security and Cooperation in Europe.