TOKYO - Japan said on Friday it will not join any U.S. coalition to protect merchant vessels in Middle Eastern waterways, but will instead send a separate force of ships and planes to guard ships supplying Japan from the key oil-producing region."We won't join the United States, but will cooperate closely with them," Japan's Chief Cabinet Secretary Yoshihide Suga told a news briefing. "Self Defense Force assets will ensure the safety of vessels related to Japan."Although it is the closest Asian ally of the United States, Japan has been reluctant to join forces with Washington in the Middle East because it maintains close diplomatic and economic ties with Iran. Tokyo has offered to act as a intermediary between the two countries to help ease tension in the region.Iran has criticized U.S. efforts to set up a coalition and says countries in the region can protect key waterways used by oil tankers supplying much of the world's oil.Military assets Japan sends to the Middle East are likely to include warships and aircraft that will patrol the Gulf of Oman, the Northern Arabian Sea and other waters in the area, Japan's chief government spokesman said. Japan has yet to decide the make up of the contingent or when it will deploy the force, he added.