North Korea faced a chorus of condemnation on Tuesday for its latest ballistic missile tests but declared that ongoing joint U.S.-South Korea military exercises were aimed at conducting a "pre-emptive nuclear attack" against Pyongyang.

Ju Yong Choi, a North Korean diplomat, told the U.N.-sponsored Conference on Disarmament in Geneva that the annual drills were "a major cause of escalation of tension that might turn into actual war" on the divided Korean peninsula.

"The ongoing joint military exercise is carried out with massive mobilisation of troops, unprecedented in size, and various types of U.S. strategic forces including nuclear carriers, nuclear strategic bombers and Stealth fighters," Ju told the 61-member forum.

"It will certainly jeopardise peace and stability in the region and drive the situation in the Korean peninsula to the brink of nuclear war," he said.

During the stormy 90-minute session, envoys from more than a dozen countries, including North Korea's main ally China, as well as Britain, France, Russia and the United States, condemned North Korea's test-firing of four ballistic missiles on Monday.

Robert Wood, U.S. Disarmament Ambassador, condemned North Korea's tests as its latest violation of U.N. Security Council resolutions. Pyongyang's weapons programme represented a "clear threat to the national security of every country of the region", he said.

The United States had an "iron-clad commitment to defend its allies" and the joint military exercises carried out with Seoul for more than 40 years were "transparent and defence-oriented".

Referring to the Democratic People's Republic of Korea (DPRK), Wood said: "It should be very clear to the DPRK that it is a pariah, it is an outlier, it is in violation of multiple U.N. Security Council resolutions, and that the countries represented in this room are not going to stand by and just let the DPRK violate international law."