WASHINGTON (AFP) - US President George W. Bush and his Chinese counterpart Hu Jintao pressed North Korea Wednesday to come clean over its nuclear arms program as South Korea warned that time and patience were wearing out on Pyongyang.

In a day of intensive diplomacy, the White House said Bush telephoned Hu to help get North Korea to make a full declaration of its nuclear arms program, while Secretary of State Condoleezza Rice met with her South Korean counterpart to keep up the heat on the Stalinist state.

"The two presidents pledged to continue to work closely with the other six-party partners in urging North Korea to deliver a complete and correct declaration of all its nuclear weapons programs, and nuclear proliferation activities and to complete the agreed disablement," a statement said.

"Bush expressed appreciation to President Hu for the important role China has played within" the six-party talks, which it chairs and are aimed at ending North Korea's nuclear weapons drive, added the statement.

North Korea has refused to make a "complete and correct" declaration of its nuclear weapons program and alleged proliferation activities as part of an aid-for-disarmament deal agreed to by the six parties -- the United States, China, the two Koreas, Japan and Russia.

"It's time to bring this to a conclusion," Bush's national security adviser Stephen Hadley said of the ongoing effort by the parties to get North Korea to come forward with a full declaration. "This has been going on for a while."

The declaration was supposed to have been made by the end of 2007 under the nuclear deal, which would reward North Korea with energy aid as well as diplomatic and security guarantees.

North Korea, which has already closed its main nuclear reactor complex and is in the process of disabling it as part of the six-party pact, submitted a list last November.

But the United States says it has not accounted fully for a suspected uranium enrichment program and allegations of nuclear proliferation to Syria.

"It was time, I think, for the president to signal to Hu Jintao that it's time for all of the parties of the six-party talks, including China, to re-engage with North Korea," Hadley told reporters.

Rice said Pyongyang's reluctance to provide the declaration was holding up the six-party talks, which had to lay the groundwork for North Korea to dismantle its nuclear arsenal -- the final phase of its denuclearization effort which Washington wants concluded before Bush retires in January 2009.

"It is really time now for there to be movement on the declaration so that with that declaration we have, we can move forward on the next phase," Rice told reporters after talks with South Korean foreign minister with Yu Myung-Hwan.

"I think time and patience is running out," Yu warned.

"I hope North Korea will submit the declaration as soon as possible so as not to lose good timing," he said.

Rice said the declaration and any associated documents should show the full range of the North Korean nuclear programs and activities "so that there can be an effort to verify and to deal with anything that has happened concerning North Korean programs and proliferation and the like.

"We've been concerned about North Korean proliferation for quite a long time. The six-party framework should be able to deal with this problem or these problems so that we can stay on course to the denuclearization of the Korean peninsula," she said.

The two ministers also discussed a proposed visa waiver program for South Koreans visiting the United States and agreed to expedite the process.

"I hope it will be done as quickly as possible, hopefully within this year," Yu said.

His Washington trip was also to prepare for an upcoming summit between Bush and South Korean presidents Lee Myung-Bak.

Lee, who took office last month, will meet Bush at Camp David from April 18-19, an encounter which Seoul hopes will strengthen the decades-old alliance.

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