U.S. Secretary of State John Kerry warned Wednesday that North Korea will face "severe consequences" if it forges ahead with irresponsible provocations, a day after Pyongyang apparently threatened a nuclear test.

"There will be severe consequences as we go forward if North Korea does not refrain from its irresponsible provocations that aggravate regional concerns, make the region less safe, and if it refuses to live up to its international obligations," Kerry said.

"Our position is clear: We will not accept a DPRK -- North Korea -- as a nuclear weapons state, just as we said that about Iran," he told reporters after talks with South African Foreign Minister Maite Nkoana-Mashabane at the State Department.

Kerry issued the warning a day after North Korea declared that its bomb-making nuclear facilities at the Yongbyon complex have returned to normal operation and apparently threatened to conduct its fourth nuclear test and a long-range rocket launch.

Asked what "severe consequences" would be, Kerry said China has taken "serious steps" to pressure the North last year and the U.S. is encouraging Beijing to do more.

"There is a process by which additional pressure is being applied to the North. And obviously, I think we've already had discussions about the potential of what may have to now be done, if indeed the DPRK's media reports and others prove to be true regarding their nuclear facilities at Yongbyon and the plutonium production reactor facility also near Yongbyon," Kerry said.

Kerry also said the U.S. and its partners in six-party talks will "continue to put pressure on North Korea in order to get them to come to a place where they understand that their people and their country can never move forward until they have lived up to their international obligations."

Kerry said economic sanctions alone may not be enough as the North is already impoverished and isolated.

"It may take more than sanctions with respect to North Korea because of its almost total absence of a legitimate economy, but nevertheless, we are talking with China, we are talking with Russia, we are talking with our friends in South Korea and Japan and elsewhere about how to proceed forward in a way that can find a peaceful and diplomatic resolution to North Korea's violation of all of the U.N. Security Council resolutions," he said.

Kerry also said he and Russian Foreign Minister Sergey Lavrov discussed the issue when they spoke by phone Tuesday.

"I can assure you that all of these countries remain fixated on the need for North Korea to denuclearize with respect to its weapons program and to live up to its international obligations.

And we will continue to calibrate, as we did with Iran by the way, the increase of particular choices that are available to us in an effort to get back to talks," he said. (Yonhap)