South Korean officials will make a rare visit to North Korea on Thursday to check Pyongyang's progress in sticking to an international nuclear disarmament deal, officials in Seoul said.

The trip will be the first high-level South Korean government delegation to visit Pyongyang since President Lee Myung-bak took office in February 2008 and is one of a handful of nuclear teams from the South ever to visit the North.

North Korea threatened to reject all attempts to inspect the core of its nuclear arms programme, with the foreign ministry saying in a statement on Tuesday that the United States must first end its "hostile policy" toward Pyongyang.

Relations between North and South Korea have chilled over the past year, with Pyongyang cutting almost all ties with Seoul in anger at the policies of Lee, who ended the free flow of unconditional aid that once headed to his destitute neighbour.

The South Korean foreign ministry said on Tuesday the team would inspect nuclear fuel rods at the North's ageing reactor as part of steps called for in a stalled disarmament-for-aid deal Pyongyang signed with five regional powers in 2005.

North Korea agreed to the visit during the last round of the six-way talks in Beijing in December.

The visit also comes after North Korea appeared to have extended an olive branch to U.S. President-elect Barack Obama by saying in a New Year's message that it was willing to work with countries that were friendly towards it.

South Korean media this week said the North had asked to send a top nuclear envoy to Obama's inauguration.

"Our team of inspectors aim to take part in the decision on the handling of unused fuel rods possessed by North Korea and will focus on technical and economic aspects in their work," the ministry said in a statement.

The team will discuss the possible purchase of unused fuel rods, local media quoted an unnamed foreign ministry official as saying at a news briefing. The ministry, which barred foreign media from attending, later confirmed the report.

North Korea has been in talks with the five countries for over a year on what to do with about 14,000 unused fuel rods including selling them for cash, a government official told reporters on condition of anonymity.

SHRINKING ECONOMY

The United States last month called for a halt in heavy fuel oil aid to punish the North for failing to agree to a system to verify the claims it made about its nuclear arms programme, considered one of the region's greatest security threats.

Analysts said the energy-starved North, whose economy is smaller now than it was 20 years ago, could see a downward slide in production if it lost out on the fuel aid promised to it as a part of the nuclear deal it reached with China, Japan, Russia, South Korea and the United States.

North Korea has had direct talks with the South in the past year as part of the six-party process, including discussions on its provisions for shipments of fuel oil and other aid.

The two Koreas are technically still at war because their 1950-1953 conflict ended in a truce and not with a peace treaty.

The South Korean team led by Hwang Joon-kook would fly into North Korea from Beijing and is expected to visit the communist state's main nuclear complex in Yongbyon, about 100 km (60 miles) north of the capital, Pyongyang.

South Korea has been pushing for talks with the North after the sputtering nuclear disarmament process hit another snag late last year after Pyongyang refused to accept a proposal to allow inspectors to take nuclear samples out of the country.