South Korea and the U.S. rejected North Korea's proposal to start peace talks to formally end the Korean War, with Seoul saying Tuesday that can happen only after the North rejoins disarmament talks and reports progress in denuclearization.

The North said Monday that its return to six-nation negotiations on its nuclear weapons program hinges on building better relations with the United States by starting peace treaty talks. The North also called for the lifting of international sanctions against it.

On Tuesday, South Korea's defense chief said he believes peace treaty talks can take place only after the nuclear talks are resumed and the North takes steps toward disarming its atomic programs.

"I think it's an issue that we can probably move forward with after the six-party talks are reopened and there is progress in North Korea's denuclearization process," Defense Minister Kim Tae-young told reporters.

He said South Korea will continue to try to find what the North's true intention is behind its peace talks proposal.

But Kim said his military is ready to deter any possible North Korean aggression, saying the North "many times in the past offered peace gestures with one hand while on the other committed provocations."

U.S. State Department spokesman P.J. Crowley also brushed off the North's call, saying it must first rejoin the six-party negotiations.

Crowley, speaking Monday in Washington, urged North Korea to return to the talks "and then we can begin to march down the list of issues that we have."

Washington and Pyongyang have never had diplomatic relations because the 1950-53 Korean War ended in a truce, not a peace treaty, thus leaving the peninsula technically at war. North Korea, the U.S.-led United Nations Command and China signed a cease-fire, but South Korea never did.

North Korea, which claims it was forced to develop atomic bombs to cope with U.S. threats, has long demanded a peace treaty. But South Korea has also been suspicious that its rival is using the issue as a distraction, while the U.S. has resisted signing a treaty while the North possesses nuclear weapons.

However, President Barack Obama's special envoy, Stephen Bosworth, said following a landmark trip to Pyongyang last month that the subject can be discussed as part of the six-nation nuclear talks, which have not been held for more than a year.

The North quit those talks with the U.S., South Korea, China, Russia and Japan last year in anger over international condemnation of a long-range rocket launch. The country later conducted its second nuclear test, test-launched a series of ballistic missiles and restarted its plutonium-producing facility, inviting widespread condemnation and tighter U.N. sanctions.

After months of tension, however, the North said last month it understood the need to resume the nuclear talks following Bosworth's trip to Pyongyang. Still, the country did not make a firm commitment on when it would rejoin the forum.

The North's statement called for a peace treaty to be concluded this year, which it emphasized marks the 60th anniversary since the outbreak of the Korean War.