Japan is considering a partial lifting of its ban on arms exports so it can sell weapons parts to the United States as it prepares for joint development of a missile-defense system, government officials said Thursday.

"It's an issue to consider in the future," Chief Cabinet Secretary Yasuo Fukuda told a news conference.

"There is a debate over whether we can simply say we cannot offer our knowhow, products or parts (to the United States) after (jointly) conducting research and development" of a missile-defense system.

"This problem has been debated for some time now," Prime Minister Junichiro Koizumi told reporters. "We will continue considering" revising the ban.

According to government sources, Fukuda plans to release a statement Friday in which he will refer to the possibility of reviewing the export rule as "a future task" for bilateral defense cooperation.

Japan has been studying missile-defense systems with the U.S. since 1998, and is planning to jointly develop a new system.

The nation adopted a ban on arms exports primarily to communist countries in 1967 and widened it to include all countries in 1976.

However, the ban was partly lifted in 1983 to allow technological cooperation with the U.S., with which Japan has a security treaty.

The latest move comes as the government is set to formally approve at a Cabinet meeting Friday the purchase of a new missile-defense system from the United States.

The government will buy Standard Missile-3 and the Patriot Advanced Capability-3 missiles to guard against possible ballistic missile attacks by North Korea.

SM3 missiles are launched from Aegis destroyers. If they fail to intercept an incoming missile, the land-based PAC3 missiles act as the last line of defense.

Koizumi stressed the importance of introducing a missile-defense system in Japan to boost Japan's defense capabilities.

"By considering both the effectiveness and the costs (of introducing the system), I believe it's necessary to have it," Koizumi said. "It goes in line with Japan's principle of using force strictly for defense purposes."