The top US negotiator on North Korea's nuclear program said Monday that it was becoming difficult for Pyongyang to meet a mid-April deadline to close a nuclear reactor, but Washington would not accept a partial shutdown.

Speaking to reporters in Tokyo, Assistant Secretary of State Christopher Hill urged Pyongyang to take agreed steps towards denuclearization regardless of a dispute over the transfer of frozen funds to North Korea.

"Clearly we are aiming for a complete fulfillment of the February agreement and we'd like to get it done by day 60," Hill said, referring to a February 13 agreement that gave the North 60 days to shut its nuclear facilities in return for energy aid.

"But obviously that timeline is becoming difficult, but certainly there is no such thing as partial," added Hill, when asked if a partial shutdown of the reactor would be acceptable.

Hill met Japanese officials later Monday. He is due to visit the Republic of Korea and China for more talks on the nuclear issue.

North Korea walked out of Six-Party Talks aimed at ending its nuclear weapons program last month when the transfer of US$25 million in funds held at Banco Delta Asia (BDA) in Macao failed to go through.

But Japan's top government spokesman said the fund dispute should not hold up implementation of the February agreement among the two Koreas, the United States, Japan, China and Russia.

Richardson in Pyongyang

New Mexico Governor Bill Richardson, who heads a delegation of US lawmakers currently visiting Pyongyang, said separately he believed the North was ready to end its nuclear weapons program and improve relations with Washington.

"I believe for the first time they do want to enter into an agreement with the six-party countries and they want a better relationship with the United States," Richardson, a Democratic presidential candidate who also visited North Korea in the 1990s and in 2005, told US broadcaster NBC.

"They know that the key is dismantling their nuclear weapons."

North Korea's top nuclear negotiator told Richardson Monday that his government would immediately invite UN nuclear inspectors into the country if the US$25 million funds are released.

North Korean Vice-Foreign Minister Kim Kye-gwan met with Richardson and Anthony Principi, US President George W. Bush's former veteran affairs secretary, in Pyongyang Monday.

Kim "indicated that the North Korean government would invite the... inspectors back the moment the funds are released to the North Korean government," Principi told reporters after the meeting.

Kim also told the US delegation that it would be difficult to shut down the country's main nuclear reactor by a Saturday deadline called for in a February nuclear disarmament accord, he said.

"They can make a beginning, but whether they can completely shut down a nuclear reactor in such a short time would be very difficult," Principi said.

(China Daily via agencies April 10, 2007)