The United States and Japan on Monday studied counter-measures to take if North Korea goes ahead with a threatened rocket launch as they renewed calls for the communist state to halt its plan.

Senior Japanese diplomat Shinsuke Sugiyama said after talks in Washington that Tokyo was seeking a coordinated international response to the launch, which North Korea plans to carry out between April 12 and 16.

"We are urging (North Korea) not to do what they announced," Sugiyama, the top Japanese diplomat for Asian affairs, told reporters.

"Of course, I don't think I'll try to deny that we are discussing the contingency measures, which means... trying to make measures if the launch is going to materialize," he said.

Sugiyama declined to go into detail on repercussions for North Korea. The United States and Japan have spearheaded efforts at the United Nations to reprimand North Korea following previous nuclear and missile tests.

North Korea said it plans to put a "satellite" into orbit to mark the 100th anniversary of the birth of the regime's founder, Kim Il-Sung, despite agreeing to a freeze on missile and nuclear tests under a February 29 deal with Washington. Kim Il-Sung died in 1994.

The United States has already suspended plans to provide North Korea with badly needed food assistance.

Japan, which has been officially pacifist and never fired a shot in anger since World War II, has said it is ready to shoot down the rocket if it poses a threat to its territory.

State Department spokesman Mark Toner said Friday that the United States understood Japan's concerns, which is why it is "telling North Korea that this planned launch is a mistake, that they should back away from it."

Sugiyama met in Washington with his US counterpart Kurt Campbell and Glyn Davies, the coordinator of US policy on North Korea.