North Korea (search) rejected a key U.S. demand Tuesday for easing nuclear tensions and threatened to link the withdrawal of U.S. troops from South Korea to a settlement, as the communist country tried to bolster its hand ahead of talks on the dispute.

Pyongyang dismissed as "unrealistic" the stance by Washington that North Korea verifiably and irreversibly dismantle its atomic weapons programs as a first step in resolving the 17-month standoff, according to the communist country's official KCNA news agency.

U.S. insistence that North Korea "completely, verifiably and irreversibly" begin dismantling its nuclear programs before receiving concessions was a key sticking point in last month's six-nation talks aimed at brokering a deal.

The talks bogged down over differences about what nuclear projects would be subject to being dismantled and how that would be verified. They ended without a major breakthrough.

North Korea blamed the outcome on an "unrealistic old assertion that the DPRK should scrap its nuclear program first," adding that a change in "U.S. attitude is a prerequisite to the settlement."

DPRK stands for Democratic People's Republic of Korea, North Korea's official name.

North Korea also reiterated that it may pin the withdrawal of U.S. troops from South Korea to the nuclear talks and demand a "verifiable and irreversible" security guarantee from Washington.

"Now that the U.S. persistently forces a complete, verifiable and irreversible dismantlement of nuclear program upon the DPRK, the latter cannot but demand the former guarantee a complete, verifiable and irreversible security, the core of which is the total withdrawal of the U.S. troops from South Korea," the KCNA report said.

North Korea has said it is willing to give up its nuclear program in return for energy and economic aid, as well as a U.S. guarantee that it will not invade.

The communist country frequently demands that the United States remove its troops from South Korea, but attaching them to the nuclear issue is a new move. The United States keep 37,000 soldiers in South Korea as a legacy of the 1950-53 Korean War.

The new demands, if brought to the negotiating table, could complicate the next round of six-nation talks between the United States, the two Koreas, China, Russia and Japan. The sides agreed to meet again before July and plan to form a lower-level "working group" to work out the details.

North Korea frequently accuses the United States of planning an attack and has asked Washington for a written security guarantee. Washington says it has no plans to invade and has offered to put something on paper.

A verifiable and irreversible security guarantee, however, could be akin to a security treaty — something many in Washington oppose.