Tokyo and Washington signed an amendment Friday to a bilateral agreement governing reciprocal provision of logistics support, supplies and services between the Self-Defense Forces and the U.S. forces stationed in Japan.

The amendment to the Acquisition and Cross-Servicing Agreement allows the SDF and the U.S. forces to share ammunition for the first time, though the provision is limited to cases in which they jointly defend Japan from a foreign attack.

The government had excluded ammunition and weapons from the list of goods that can be shared between the SDF and the U.S. for fear that it could violate Japan's self-imposed ban on arms exports, a rule Tokyo introduced under its Constitution.

Chief Cabinet Secretary Yasuo Fukuda said Friday the amendment does not violate the rule, which "was intended to avoid escalation of international conflicts."

He said ammunition would "only be supplied to the U.S. forces, and the U.S. is obliged not to use it against the spirit of the U.N. Charter and not to hand it over to a third nation without the consent of our government."

The amendment also allows the SDF and U.S. forces to cooperate on logistics when conducting activities that would "contribute to international peace and security."

These activities do not exclude actions by multilateral forces unauthorized by the U.N., an agency official said.

This means the SDF could offer logistic support in cases such as the U.S.-led war on Iraq and reconstruction efforts. Although providing ammunition to such forces is not stipulated in this case, the government believes it would be possible if a new law was enacted for each case.

The amendment was part of Japan's efforts to update security laws to reflect the war contingency legislation, passed in June, which defined the government's steps to mobilize the SDF in the event of an attack on Japan.