TOKYO (Reuters) - Japan on Wednesday said it plans to offer friendly nations financial assistance to help them bolster their defences, marking Tokyo's first unambiguous departure from rules that forbid using international aid for military purposes.

Japan's Overseas Security Assistance (OSA) will be operated separately from the Overseas Development Assistance (ODA) programme that for decades has funded roads, dams and other civilian infrastructure projects, Chief Cabinet Secretary Hirokazu Matsuno said at a regular news conference.

"By enhancing their security and deterrence capabilities, OSA aims to deepen our security cooperation with the countries, to create a desirable security environment for Japan," a statement released by the Ministry of Foreign Affairs on Wednesday said.

The aid will not be used to buy lethal weapons that recipient countries could use in conflicts with other nations in accordance with the three principles that govern arms exports, according to the statement.

The Philippines and Bangladesh are likely to be included as the first recipients of the aid, a government source involved in talks said to Reuters.

Japan is considering providing radars to the Philippines to help it monitor Chinese activity in the contested South China Sea, and also weighing Fiji and Malaysia as potential recipients of the aid, the Yomiuri newspaper reported on Monday.

In principle, only developing countries will be eligible to receive the aid given it will be provided as grants, according to the foreign ministry.

The decision to expand the scope of international aid to military-related projects follows Japan's announcement in December of a military build up that will double defence spending within five years as it looks to counter China's growing military might in Asia.

(Reporting by Tim Kelly, Yukiko Toyoda, Sakura Murakami, and Chang-Ran Kim; Editing by Tom Hogue, Christian Schmollinger and Raju Gopalakrishnan)