North Korea announced last month it was planning a mid-April deployment of an Earth observation satellite using a long-range rocket. The announcement followed a pledge to halt launches and nuclear work in exchange for food assistance from the United States.
Washington had said the announcement was a provocative act while Tokyo said it would shoot the rocket down should its flight path cross Japanese territory.
U.S. Secretary of Defense Leon Panetta spoke by phone with Japanese Defense Minister Naoki Tanako about the announced launch.
"Secretary Panetta and Defense Minister Tanaka reiterated their view that such a missile launch would directly violate North Korea's international obligations and U.N. Security Council Resolutions 1718 and 1874," acting Assistant Secretary of Defense for Public Affairs George Little said in a statement.
"They also affirmed the importance of the U.S.-Japan alliance in defense of Japan and in contributing to regional peace and security."
Tokyo this week extended sanctions on Pyongyang for another year. North Korea said last week it was committed to the launch despite the international pressure.