Six-nation talks on North Korea''s nuclear program that are set to resume in the Chinese capital on Thursday may run into disagreements over key issues, Russia''s chief nuclear negotiator has said.

The six-party talks, including Russia, the United States, China, Japan and the two Koreas, will be held in Beijing from July 10-12. They were stalled late last year when Pyongyang missed a deadline to hand over nuclear data as part of a deal under which the North was promised economic aid and diplomatic incentives.

However, the talks were given new life when North Korea handed over detailed data on its nuclear activities in late June. It also demolished on June 27 the cooling tower at its main Yongbyon nuclear complex, about 100 km (62 miles) north of Pyongyang. The disabling of facilities at the plant is being monitored by U.S. specialists.

"Disagreements may emerge on the verification of the declaration [of nuclear activities] submitted by North Korea to the Chinese side and eventually disseminated among the parties to the six-nation talks," Alexei Borodavkin said on Wednesday upon his arrival in Beijing.

North Korea has said that it only possesses 37 kilograms of plutonium and has destroyed the means to make more.

According to Borodavkin, the second controversial issue could be supplies promised to North Korea in exchange for its pledge to curtail its nuclear activities. At the same time, Borodavkin said Russia was honoring its commitments to supply heating oil supplies to North Korea.

"We have done what we promised, having supplied 100,000 metric tons [of heating oil] in two batches of 50,000 metric tons each by mid-year," Borodavkin said.

According to the South Korean news agency, Yonhap, the six-nation consultations in the Chinese capital will focus on an appraisal of the data handed over by North Korea, the elaboration of a method of the verification of the nuclear data, and a date for a meeting of the foreign ministers from the six nations.

After the North submitted its nuclear declaration, the U.S. announced it would lift unilateral trade sanctions against the country and remove it from a terrorism blacklist.

However, U.S. President George Bush said Washington continues to be concerned over North Korea''s uranium enrichment activities and suspected sales of nuclear technology to other countries.