GENEVA — Brushing off widespread condemnation of its nuclear test earlier month, North Korea rebuked the United States on Wednesday for destabilizing the Korean Peninsula and fueling an “explosive situation” by its persistent hostility toward Pyongyang.

“The U.S. is to blame for the situation on the Korean Peninsula, which is inching close to an unpredictable phase now,” North Korea’s representative to the United Nations in Geneva, So Se Pyong, told the Conference on Disarmament in Geneva, capping a week of fiery rhetoric from Pyongyang targeting Washington and Seoul.

Mr. So stirred up the normally staid proceedings of the United Nations-supported forum on disarmament last week by threatening South Korea with “final destruction.” Three days later, North Korea warned United States forces in South Korea that they faced “miserable destruction” if they proceeded with joint military exercises with South Korean troops due to take place in March.

In his statement on Wednesday, Mr. So suggested that North Korea’s third nuclear test had been a defensive move provoked by American hostility to the North’s launching of a satellite in December. The United Nations Security Council toughened sanctions against North Korea after the launching, which was seen as another step toward developing a ballistic missile with an intercontinental range that could carry a nuclear warhead.