SEOUL, South Korea (AP) - North Korea vowed Tuesday to strengthen its nuclear deterrent and its means of delivery - an apparent reference to missiles - days after threatening rival South Korea and U.S. forces with attack if they conduct military exercises as planned next week.

The threat comes as the U.S. and other dialogue partners are pushing for the North's communist regime to rejoin disarmament talks it pulled out of last year in anger over international condemnation of a long-range rocket launch. Soon after, it conducted its second atomic test - a move that drew tighter U.N. sanctions.

The North's official Korean Central News Agency said Tuesday there will be no progress in denuclearization on the Korean Peninsula unless the U.S. removes its nuclear threat against the North.

The U.S. denies posing such a military threat to the North, although it retains about 28,500 troops in South Korea.

The North wants sanctions lifted and peace talks to formally resolve the 1950-53 Korean War - which ended in a truce, not a peace treaty. The U.S., South Korea and Japan have responded the North must first return to the disarmament talks and make progress on denuclearization.

"Should the U.S. persist in its unrealistic moves to stifle the (North) in disregard of its realistic proposal, this will only compel it to boost its nuclear deterrent and its delivery means," the KCNA dispatch said.

The North routinely issues threats about its nuclear deterrent, but it is the first time it has referred to how it would deliver a nuclear weapon.

The North is believed have enough weaponized plutonium for at least half a dozen atomic bombs, and has been developing a long-range missile designed to strike the U.S. Experts say, however, it has not mastered the technology required to mount a nuclear warhead onto the missile.

The statement comes ahead of annual U.S.-South Korean military drills starting in South Korea next Monday. Last week, the North threatened a "powerful" - even nuclear - attack if the drills go ahead.

The North says the exercises are preparation for an invasion, but the U.S. and South Korea say the maneuvers are purely defensive.

Despite that dispute, officials from the two Koreas held talks Tuesday on easing border crossings, communication and customs clearance for South Koreans who work at a joint industrial complex in the North.

The two sides failed to produce any specific agreement during the talks at the complex in Kaesong, but will meet again, South Korean Unification Ministry spokeswoman Lee Jong-joo said, without elaborating.

The Kaesong complex is the most tangible sign of cooperation on the divided peninsula. It has combined South Korean capital and know-how with cheap labor from cash-strapped North Korea, with about 110 South Korean factories employing 42,000 North Korean workers.