VIENNA - UN inspectors are now set to travel to North Korea and will be leaving in the "next few days," the International Atomic Energy Agency said Tuesday, after receiving a formal invitation from Pyongyang.

The International Atomic Energy Agency (IAEA) chief Mohamed ElBaradei gives a press conference the IAEA's 35-nation board of governors meeting at the organization's headquarters in Vienna, 09 July 2007. [Agencies]

The IAEA's 35-nation board of governors had approved Monday sending inspectors back to North Korea for the first time since 2002 to verify the first steps by Pyongyang in dismantling its nuclear weapons programme, a process that is expected to be long and difficult.

The inspectors could not leave until North Korea formally invited the IAEA to send them, and the invitation shows Pyongyang moving quickly at this point to meet its obligations.

The larger negotiating process is also proceeding. Six-nation talks on scrapping North Korea's nuclear programme are likely to resume next week, South Korea said Tuesday.

"The key thing here is not simply getting this first stage agreement completed but then continuing on with disabling and ultimately dismantling of the North Korean nuclear program," US State Department Tom Casey said in Washington.

The mission will re-establish international monitoring nearly five years after the agency was kicked out in December 2002 when Pyongyang moved to re-start its Yongbyon reactor.

The reclusive, Stalinist state conducted its first nuclear test in October last year. It is believed to have several plutonium bombs.

North Korea has now agreed to shut down Yongbyon, in a six-party agreement reached on February 13. The accord, which secures fuel supplies for North Korea, is a first step towards Pyongyang giving up its nuclear weapons.

The IAEA said in a statement that "following receipt of an invitation today (Tuesday) from the Democratic People's Republic of Korea an IAEA team will travel to the DPRK within the next few days."

It did not say exactly when this would be but diplomats have said a nine-member mission could be leaving Saturday, or possibly as early as Thursday.

Pyongyang is waiting for a shipment of fuel from South Korea as a first payment in the six-party deal reached with China, Japan, South Korea, Russia and the United States.

Energy-starved North Korea is getting 50,000 tonnes of oil from South Korea in return for closing Yongbyon, and the first shipment is due to be sent Thursday.

The IAEA said its "team will implement arrangements agreed between the IAEA and the DPRK and approved by the agency's Board of Governors to undertake verification and monitoring of the shutdown and sealing of DPRK's Yongbyon nuclear facilities."

IAEA chief Mohamed ElBaradei had said Monday that "shutting down the facilities ... should not take much time, probably a few days" but then surveillance cameras and other equipment would have to be installed.

The site includes the five-megawatt Yongbyon research reactor plus two other power reactors under construction, a reprocessing plant and a fuel fabrication plant.

The IAEA board on Monday granted ElBaradei 1.7 million euros (2.3 million dollars) in 2007 and 2.2 million euros in 2008 for "the monitoring and verification activities" in North Korea.

ElBaradei said there should be no problem in getting the money, since the United States has already committed millions of dollars. He said he expected "a number of countries" to contribute.

Diplomats said the IAEA would be maintaining a "permanent two-person inspector presence at Yongbyon" once the mission there resumes.

ElBaradei visited North Korea in March to set up IAEA monitoring there but a banking dispute over millions of dollars blocked by US sanctions delayed the closing of Yongbyon beyond what was supposed to be an April 13 deadline.