Chinese diplomats hosted talks on the issue last August in Beijing with their counterparts from the United States, Japan, South Korea, Russia and North Korea. Bush and Wen are pushing for a second round of the six-party talks, but Wen told him on Tuesday that conditions were not yet ripe for such a meeting.

The United States has floated a draft proposal on the matter, hoping to draw North Korea back to the negotiating table.

North Korea's communist government said Tuesday it was willing to "freeze" its nuclear program while talks continue. Bush rejected that position.

"The goal of the United States is not for a freeze of the nuclear program," Bush said. "The goal is to dismantle a nuclear weapons program in a verifiable and irreversible way. And that is a clear message that we are sending to the North Koreans."

Bush and Wen also discussed the issue of China's currency, which is pegged to the U.S. dollar in a way that some economists think artificially deflates the value of the Chinese yuan. That has the effect, critics say, of making Chinese exports to the United States cheaper than they would otherwise be, while making U.S. products more expensive in China.

The two leaders agreed to assign senior diplomats to meet in January to discuss ways to deal with the issue. Interim steps under discussion, short of a free-floating exchange rate, are aimed at making the yuan more flexible.