North Korea on Tuesday rejected a U.N. Security Council resolution imposing tougher sanctions and said the United States would soon face the “greatest pain” it had ever experienced.

The Security Council unanimously stepped up sanctions against North Korea on Monday over the country’s sixth and most powerful nuclear test, imposing a ban on its textile exports and capping imports of crude oil.

“My delegation condemns in the strongest terms and categorically rejects the latest illegal and unlawful U.N. Security Council resolution,” Pyongyang’s ambassador, Han Tae Song, told the U.N.-sponsored Conference on Disarmament in Geneva.

Han accused the U.S. administration of being “fired up for political, economic, and military confrontation,” and of being “obsessed with the wild game of reversing the DPRK’s development of nuclear force which has already reached the completion phase.”

North Korea was condemned globally for its latest nuclear test on Sept. 3, which it said was of an advanced hydrogen bomb.

The Democratic People’s Republic of Korea (DPRK) is “ready to use a form of ultimate means,” Han said without elaborating.