US envoy Christopher Hill, recently named Washington's senior delegate to six-party talks on the North Korean nuclear stand-off, said he had no advice to give Seoul on how to respond to Pyongyang's recent request for 500,000 tonnes of fertilizer aid.

"I'm certainly not going to be giving advice to the ROK," said Hill, who also serves as the US ambassador to South Korea, speaking at a seminar.

"What we need to do is to coordinate our approaches and make sure that the DPRK does not try to exploit any differences among any of the partners in the six-party process."

Agricultural experts say the amount is close to North Korea's entire yearly requirements in fertilizer. In recent years South Korea has supplied around 300,000 tonnes annually to North Korea.

The request comes as Washington stepped up pressure on North Korea following Pyongyang's statement last week that it had nuclear weapons and was turning its back on international dialogue.

South Korea has been pushing ahead with an engagement policy with North Korea throughout the more than two-years-old nuclear standoff, upsetting hawks in the Bush administration who champion a harder line against Pyongyang.

While meeting with South Korean Foreign Minister Ban Ki-Moon in Washington last week, Deputy Defense Secretary Paul Wolfowitz said South Korea should "underreact" to the fertilizer aid request, Yonhap news agency said Thursday, quoting diplomatic sources in Washington.

The New York Times reported that US Vice President Dick Cheney told Ban in a meeting on Sunday that South Korea should reject the fertilizer aid.

On his return from Washigton on Wednesday, Ban said, however, that US officials made no comment or proposals concerning South Korea's reaction to the aid request.

He said Seoul would consider "varying circumstances" before making a final decision on this issue.

Hill, who made a one-day trip to China on Thursday, also said China and the United States had reached an "absolute agreement" that North Korea must return to dialogue at an early date to end its nuclear ambitions peacefully.

"We had a very good discussion about the six-party process and the absolute agreement on the need for North Korea to come back to the process," he said.

"We will try to construct an agreement that will enable them to get out of the weapons, out of the nuclear weapons business, and into the business of trying to develop their economy and trying to integrate the rest of the world, which is the only outcome that any person should want for the DPRK," he said.

Hill and South Korea's chief negotiator, Deputy Foreign Minister Song Min-Soon, held separate meetings with Chinese Foreign Minister Li Zhaoxing and leading Chinese diplomats on Thursday.

In talks with Song, Li praised South Korean efforts at trying to improve relations with its northern neighbor, but reiterated Beijing's stance that North Korea's security concerns needed to be taken into account.

The discussions in Beijing are expected to be followed by a weekend visit to Pyongyang by Wang Jiarui, a special envoy from China, the broker and host of the six-party talks and North Korea's closest ally.

The nuclear standoff erupted in October 2002 when the United States accused North Korea of operating a weapons programme based on highly enriched uranium, violating a 1994 arms control agreement.

The last set of six-way talks -- among the two Koreas, Russia, China, Japan, and the United States -- took place in June last year but produced few results.

North Korea shunned a fourth round set for last September, complaining of "hostile" US policies.