North Korea for the first time threatened the United States with a pre-emptive nuclear strike in a bout of heated rhetoric ahead of Thursday’s United Nations vote on further sanctions.

In a statement to the Korean Central News Agency, a spokesman for the Foreign Ministry called the pending sanctions an “act of war,” The New York Times reports. The statement said ongoing joint military exercises between the U.S. and South Korea were proof the nations “aimed to mount a pre-emptive strike,” and threatened North Korea would hit first and turn Washington and Seoul into a “sea of flames.”

{mosads}“Now that the U.S. is set to light a fuse for a nuclear war,” the spokesman said, “the revolutionary armed forces of [North Korea] will exercise the right to a preemptive nuclear attack to destroy the strongholds of the aggressors and to defend the supreme interests of the country.”

While North Korea has asserted a right to pre-emptive strike in the past, this is the first time it has threatened a nuclear attack. The comments come after its traditional ally, China, announced its intention to join a new round of U.S.-led sanctions at the U.N. in response to North Korea’s third nuclear test last month. The Security Council is expected to adopt the new sanctions on Thursday.

“The sanctions contained in this draft resolution will significantly impede North Korea’s ability to develop further its illicit nuclear and ballistic missile programs,” the U.S. ambassador to the U.N., Susan Rice, said Tuesday. “These sanctions ― as well as a commitment to take further significant measures in the event of another launch or nuclear test ― will demonstrate clearly to North Korea the continued costs of its provocations.

“The resolution tabled today will take the UN sanctions imposed on North Korea to the next level, breaking new ground and imposing significant new legal obligations. For example, for the first time ever, this resolution targets the illicit activities of North Korean diplomatic personnel, North Korean banking relationships, illicit transfers of bulk cash, and new travel restrictions.”

Congress is also readying its own sanctions. The House and Senate Foreign affairs panels are both holding hearings this week on measures to block Kim Jong Un’s regime from benefiting from illegal activities such as weapons smuggling and drug trafficking, with an eye toward preparing new sanctions legislation shortly.