U.S. Defense Secretary Leon Panetta spoke with South Korea's Defense Minister Kim Kwan-jin by telephone on Monday evening to discuss North Korea's planned missile launch, a Pentagon spokesman said.
Both leaders would regard a missile launch by North Korea as a serious provocation and a violation of North Korea's international obligations and standing U.N. Security Council resolutions, Pentagon spokesman George Little said.
Earlier on Monday, the United States urged North Korea not to conduct a nuclear test or launch a satellite and it called upon China to exert its influence over its neighbor to try to ward off such provocative actions.
North Korea, which is pressing ahead with plans for a satellite launch despite U.S. and regional appeals that it desist, is also preparing a third nuclear test, South Korean news reports said on Sunday.
Another nuclear test is bound to scare neighbors and infuriate the West, which has long sought to curb the North's nuclear ambitions.
South Korea's Yonhap news agency quoted an unidentified intelligence source as saying North Korea was clandestinely preparing a nuclear test at the same location as the first two.
The State Department repeated its advice to the North not to launch a satellite, saying this would violate Security Council resolutions and a February 29 denuclearization agreement.
North Korea, which three years ago pulled out of six-party disarmament talks on its nuclear program, agreed in February to stop nuclear tests, uranium enrichment and long-range missile launches in return for food aid, opening the way to a possible resumption of the negotiations.
But that has unraveled with the North's rocket launch planned for this month. The North says it is merely sending a weather satellite into space, but South Korea and the United States say it is a ballistic missile test.
North Korean leader Kim Jong-il died in December and his son, Kim Jong-un succeeded him as leader of the autocratic state. The change of leadership was not expected to lead to major changes in North Korea's foreign or domestic policy, but Western and other Asian nations have been closely observing the secretive state for signs of a shift in policy
(Reporting by Tabassum Zakaria; Editing by Paul Simao and Todd Eastham)