SEOUL, South Korea — North Korea has vowed to bolster its nuclear force unless the United States drops its ”hostile policy” toward the reclusive communist nation, adding that its atomic program could not be traded for economic aid.

Pyongyang also designated eight new naval firing zones near its eastern and western sea borders with South Korea in a move that could raise tensions.

North Korea quit the disarmament-for-aid negotiations and conducted a second nuclear test last year, drawing tightened U.N. sanctions. North Korea has demanded a lifting of the sanctions and peace talks formally ending the 1950-53 Korean War before it returns to the negotiating table.

The North’s official Korean Central News Agency today urged the United States to make a political decision to establish peace on the peninsula and change what it calls a policy to stifle the North.

The North’s ”nuclear deterrent for self-defense will remain as ever and grow more powerful … as long as the U.S. nuclear threat and hostile policy persist,” KCNA said Friday in a dispatch from Pyongyang.

The North’s ”dismantlement of its nuclear weapons can never happen … unless the hostile policy towards the (North) is rolled back and the nuclear threat to it removed.”

North Korea claims it was compelled to develop atomic bombs to cope with U.S. nuclear threats. The United States, which denies making any such threats against the North, has called on North Korea to return to the disarmament talks that also involve China, South Korea, Russia and Japan.

The newly designated ”naval firing zones” are effective today through Monday, Seoul’s Joint Chiefs of Staff said Friday.

Last month, North Korea fired artillery shells near its disputed western sea border, prompting the South Koreans to fire warning shots. No injuries or damage were reported.