In an interview with Japan's Kyodo news service, Kim Yong Nam, president of the Presidium of the Supreme People's Assembly, the same tenet applied to returning to six-nation talks about the nuclear program.
"If the United States continues to take a hostile attitude and apply pressure on us in various forms, we will have no choice but to take physical steps to deal with that," he said, apparently alluding to more nuclear tests.
Harsher wording came from the North Korean Foreign Ministry earlier, when a spokesman said if the United States bolstered sanctions against the country, the country will interpret it as a declaration of war, Kyodo reported.
The talks, which involve the North and South Korea, China, Japan, Russia and the United States, have been stalled since last November, with the North refusing to return to negotiations unless the United States lifts existing financial sanctions.
Monday, North Korea conducted some type of test explosion underground, although its claim it was a nuclear test has not been corroborated.