"It's not bad that the resumption of nuclear talks is delayed. During that period, we will make more deterrent force," the North's top nuclear envoy, Kim Kye Gwan, told a news conference in Tokyo.
North Korea has said it has atomic weapons, although the claim has not been verified independently.
"We will react in an ultra hardline manner if the United States continues to apply pressure and sanctions. We will never yield to pressure," Kim said.
Kim said North Korea will only return to the six-nation talks on ending its nuclear weapons program if the U.S. lifts a freeze on disputed North Korean assets in a Macau bank.
"There is no compromise and flexibility on this issue," he said. "I will go to the negotiating table the moment I seize the assets with my hands."
Washington says the sanctions are unrelated to the nuclear talks and will stay in place.
It says the assets, which total about US$24 million ( Ђ 19.7 million), are linked to money laundering and counterfeiting.
Kim made the comments after several days of meetings in Japan among officials from the six nations involved in the nuclear negotiations, the U.S., China, Japan, Russia and the two Koreas, failed to win a commitment from North Korea to return to the negotiating table.
Kim left Tokyo later Thursday to return home, reports the AP.