North Korea is unleashing a new burst of harsh rhetoric against the United States. Pyongyang says Washington's actions are bringing the Korean peninsula closer to war.
North Korea's official news agency accuses the United States of stepping up aerial espionage over the past month. Pyongyang says the surveillance is a precursor to an Iraq-style pre-emptive attack by the United States.
On Tuesday, North Korea warned it would take "strong and merciless" retaliatory measures in response to any economic blockade. Pyongyang has said many times in the past it views a blockade or sanctions as a declaration of war.
A representative of the North Korean People's Army on Tuesday warned Pyongyang may withdraw from the 1953 armistice that ended hostilities in the Korean War. He said the United States would provoke a withdrawal if it applied sanctions or increased its troop presence in the South.
Washington is pushing many governments around the world to pressure North Korea to give up its nuclear weapons program, which violates several international agreements. The United States has said repeatedly it wants to end Pyongyang's nuclear programs through diplomacy and that it has no plans to invade North Korea.
The United States accuses Pyongyang of funding its operations with counterfeiting and illegal drug and weapons sales. It is working with its allies to restrict North Korea's ability to trade in contraband.
In Beijing, the government was sending a senior diplomat to Washington on Tuesday.
Foreign Ministry spokesman Kong Quan says Vice Foreign Minister Wang Yi will visit the United States until July fourth to exchange views on the situation in Asia and on the Korean Peninsula.
Also Tuesday, the New York Times cited U.S. intelligence officials, saying North Korea is trying to adapt nuclear weapons to its existing missile technology.
It gives a U.S. intelligence warning that North Korea may be able to reach both Japan and the United States with a nuclear warhead within a year.
The United States thinks North Korea may already have one or two nuclear weapons - but says Pyongyang has never conducted a nuclear weapons test.