The White House says the agreement to extend South Korea's ballistic missile range is a "prudent, proportional, and specific response" to North Korea.

White House spokesman Jay Carney told reporters on Air Force One during a flight to Los Angeles that the U.S. is in regular consultations with South Korea and the new missile guidelines are designed to improve the ability to defend against North Korea's ballistic missiles.

On concerns that the revision may heighten tensions on the Korean Peninsula, he said the onus is on North Korea, as it has been, to abide by its international obligations to fulfill its obligations under two UN Security Council resolutions. Carney stressed it was "absolutely legitimate" for South Korea to take actions in consultation with the U.S. to respond to a threat posed by North Korea's ballistic missile program.