China said on Tuesday mistrust between North Korea and the United States was the main hurdle to negotiations on the North's nuclear program as the Chinese defense minister held talks in Pyongyang.

China has been urged to persuade North Korea to agree to another round of six-party talks also involving the United States, South Korea, Japan and Russia.

"The cause of the current stalemate is the mistrust between North Korea and the United States and their differences over some specific issues," Chinese Foreign Ministry spokesman Liu Jianchao told a regular news conference.

He said all sides should stick to the goal of eventual de-nuclearization of the Korean peninsula.

"China as a major mediator has always been making active and difficult efforts," Liu said. "The progress of the six-party talks is not totally up to Chinese efforts. The key to resolving problems is in the hands of North Korea and the United States."

The six countries agreed in principle in September that the North would dismantle its nuclear programs in exchange for aid and better diplomatic ties. But their latest session in November ended without progress.

North Korea has said it would be unthinkable to return to the nuclear talks while Washington is trying to topple its leaders through action against Pyongyang's purported counterfeiting, drug trafficking and money laundering.

North Korea has denied involvement in any illegal activities.

Chinese Defense Minister Cao Gangchuan held talks on Tuesday with Vice Marshal of the Korean People's Army, Kim il-Chol, also minister of the People's Armed Forces, at a time when Pyongyang is facing strong pressure to return to the negotiations.

"The talks took place in a comradely and friendly atmosphere," the North's KCNA news agency said.

Chinese Foreign Ministry spokesman Liu said he did not know if Cao would meet North Korean leader Kim Jong-il in Pyongyang.

The two Koreas are still technically at war after their fratricidal 1950-53 conflict ended in a truce, not a peace pact.

A North Korean official will make a rare visit to Japan later this week to take part in a private forum on security issues and could have talks with negotiators to the six-party nuclear talks, diplomatic sources said on Tuesday.

And U.S. chief negotiator Christopher Hill is expected to arrive in Tokyo on Monday for talks with his counterparts from Japan and South Korea, a U.S. embassy spokesman said.

On April 15, Cao is due to lead a delegation of 18 senior military officers to the South for talks on promoting military exchanges between the two countries, South Korea's Defense Ministry said in a statement.

Cao will also meet South Korean President Roh Moo-hyun and inspect military units and industrial plants, the ministry said.