Defense Agency Director-General Yoshinori Ono and US Ambassador Howard Baker signed the agreement a week after Japan ended its decades-old ban on military exports -- but only to the United States for the defense system.

Tokyo and Washington began to study a missile interception shield after North Korea shocked the world in 1998 by firing a long-range Taepodong-1 missile over Japan.

But the previous ban prevented Japan from exporting missile components to the United States and each exchange of information to develop the shield had to be authorized by a diplomatic agreement between the two allies.

Under the memorandum of understanding signed Friday, Japan and the United States will form a committee to share information and do away with the lengthy paperwork for the research.

North Korea on Wednesday warned Japan that it would consider it to be an act of war if Tokyo imposed economic sanctions in a dispute over Pyongyang's abductions of Japanese nationals during the Cold War.

Japan has promised to take account of concerns of the United States and other countries which have told Tokyo that sanctions on unpredictable North Korea could backfire.

A US test for a future missile shield failed on Wednesday when an interceptor missile failed to go off during the exercise in the Pacific Ocean.

Japanese government spokesman Hiroyuki Hosoda said Thursday that the failure would not affect plans to build a shield for Japan as the two systems were different.

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