The threat came as the United States and China introduced new sanctions against North Korea at the United Nations. U.S. Ambassador Susan Rice told reporters the sanctions will be among "the toughest" imposed by the United Nations, The Wall Street Journal reported.
"The resolution tabled today will take the U.N. sanctions imposed on North Korea to the next level, breaking new ground and imposing significant new legal obligations," Rice said.
The ambassador said the sanctions target North Korean diplomats and Pyongyang's international banking relationships, the Journal reported. She said U.S.-Chinese agreement on the new sanctions came after "intensive and productive" negotiations and she hoped the U.N. Security Council would adopt them unanimously this week.
The North Tuesday denounced joint South Korean-U.S. military exercises scheduled to begin Monday, saying if the drills are conducted, it will sever military phone links across the border with South Korea, Yonhap News Agency reported.
The "Key Resolve" program of two weeks of military exercises is expected to involve 10,000 South Korean troops and 3,500 U.S. troops.
The Korean People's Army said it would carry out more and stronger countermeasures in response to the "hostile" policies of the United States and South Korea, an army spokesman said on North Korean state television.
North Korean leaders decided Monday to halt the work of its delegation at Panmunjom where North and South Korean delegates typically meet for communication and negotiations, China's official Xinhua news agency reported.
A Chinese Foreign Ministry spokeswoman said Tuesday Beijing expected all parties "to do more to ease tensions on the peninsula and promote regional peace and stability."
North Korea conducted its third nuclear test Feb. 12, drawing international condemnation.
U.S. Secretary of State John Kerry, in his first public comment on Dennis Rodman's so-called basketball diplomacy mission to North Korea, said the former NBA star "was a great basketball player. And as a diplomat, he is a great basketball player. And that's where we'll leave it."
Rodman, the first American to meet North Korean leader Kim Jong Un, said on ABC's "This Week" Sunday he doesn't condone Kim's practices but called him "a friend" and a great man, and suggested Kim will change North Korean policy.
"He said, 'If you can Dennis, I don't want to do war. I don't want to do war,'" Rodman said, telling ABC President Barack Obama should contact Kim because both men love basketball.
White House press secretary Jay Carney told reporters Monday Rodman's trip, which was arranged as part of a U.S. television production, has no bearing on U.S. relations with North Korea.
"And instead of spending money on celebrity sporting events to entertain the elites of that country, the North Korean regime should focus on the well-being of its own people who have been starved, imprisoned, and denied their human rights," Carney said.
"We have urged the North Korean leadership to heed President Obama's call to choose the path of peace and come into compliance with its international obligations," he said. "North Korea's actions, however, directly violate United Nations Security Council resolutions and threaten international peace and security."