The United States has told Japan that it plans to begin deploying interceptor missiles in 2008 under the countries' joint missile-defense initiative, Japanese and U.S. government sources said Friday.

The U.S. plan, unofficially conveyed to Japan, is likely to put further pressure on Tokyo to advance to the development stage of the missile-defense initiative at an earlier date.

Under a bilateral accord agreed to in September 1998, the two countries are currently conducting a joint study on a system to protect Japan -- and U.S. forces deployed in the country -- from medium-range missiles.

The study focuses on four primary components of interceptor missiles for a system employing destroyers equipped with the state-of-the-art Aegis defense system.