South Korean and U.S. officials have urged North Korea to conduct an early declaration of its nuclear programs, warning to take further steps against it.

After meeting with South Korea's main nuclear negotiator, Chun Yung-woo in Seoul, United States Assistant Secretary of State Christopher Hill says North Korea's nuclear disarmament process has "lost a lot of time," and stresses the need for forward momentum.

"I must say as difficult the declaration it is, I think the next phase would be more difficult as we try to get North Korea to finally go away with its nuclear ambitions, and so we have a lot of work to do and frankly speaking, we're really at the point where we need this declaration very soon."

Chun Yung-woo says South Korea and the United States shared the understanding that "there is no reason to wait further." He adds that the two sides have discussed further steps.

However, he refuses to disclose what the next step is.

North Korea says it submitted the declaration last November. However, the U.S. side argues the document is not complete.

Under an agreement reached last October during the six-party talks on the nuclear issues on the Korean Peninsula, North Korea has agreed to declare all its nuclear programs by the end of 2007 while the United States and other parties provide economic, energy and humanitarian assistance to North Korea.