The United States would negotiate a peace treaty with North Korea only if the communist country is ready to abandon its nuclear weapons program, a former U.S. envoy to the six-party denuclearization talks said Thursday.

Christopher Hill, who served as Washington's lead negotiator in the six-party talks on the North's nuclear program in his capacity as assistant secretary of state, said a peace treaty was an element of the September 2005 deal under which Pyongyang agreed to dismantle its nuclear program in exchange for political and economic concessions.

"It's one of our obligations, but I don't think the North Koreans can take one obligation out of the talks and expect that to be implemented and not implement anything else," Hill said as he met with reporters to discuss the recent release of the Korean language version of his memoir, "Outpost: Life on the Frontlines of American Diplomacy."

"I think the U.S. is prepared to pursue a peace treaty in the context of the denuclearization of North Korea, but the North Koreans cannot have a peace treaty and have nuclear weapons," he said.

North Korea has recently renewed its demand for a peace treaty with the U.S., claiming the armistice agreement that ended the 1950-53 Korean War does not ensure peace on the Korean Peninsula.

Both Seoul and Washington have rejected the proposal as a ploy to divert attention away from its nuclear weapons program, which they say should be dismantled first before talks for a peace treaty can begin.

Since the 2005 agreement, North Korea has resumed its nuclear program and conducted three nuclear tests. It has long threatened to carry out a fourth test.

The six-party talks, which also involve South Korea, China, Russia and Japan, have not been held since late 2008. North Korea demands an unconditional resumption of the talks, while Seoul and Washington insist it first demonstrate its commitment to its obligations.

"The time needs to be filled up with a more robust approach to China," Hill said. "We should be talking to China everyday about this problem because they need to be part of the solution."

Hill, currently dean of the Josef Korbel School of International Studies at the University of Denver, also suggested tighter cooperation between Seoul and Washington on defense.

"I think we need to be looking at the range of defensive measures that we have against these offensive military threats," he said. "I think we need to work on systems that will render the North Korean threat obsolete. There's been a lot of developments in these kinds of defensive, technological, anti-missile systems."

Hill previously served as U.S. ambassador to Seoul from 2004-2005. (Yonhap)