Japan, Britain and Italy are expected to ink a treaty in Japan next week to set up a joint organization and industry group for developing their planned advanced jet fighter, three sources with direct knowledge of the plans said.

An inter-government body will oversee the industry group venture led by Britain's BAE Systems, Japan's Mitsubishi Heavy Industries and Italy's Leonardo. That group will distribute work to teams in different parts of the Global Combat Air Programme (GCAP), such as the engine and avionics, the sources said.

They asked not to be identified because they were not authorized to speak to the media.

In March, Reuters reported that Japan and Britain would dominate GCAP, with about a 40% share of the work each. Rome dismissed that as "speculative."

Japan's Defense Ministry declined to comment. Officials at the British and Italian Embassies did not immediately respond to requests for comment.

The agreement, which parliaments of each country must ratify, will come a year after they established their first major defense industry collaboration by merging the separate next-generation fighter efforts of London and Tokyo.

Someone from Japan may lead the project initially, and the management will rotate among the three countries, two of the sources said. They added that Japan's leading candidate for that job is Masami Oka, an adviser to the Defense Ministry who retired as vice minister of international affairs in July.

Oka did not immediately respond to a request for comment.

The three countries plan to choose Britain as GCAP's headquarters, Reuters reported in September. GCAP may also welcome other nations as junior partners, with Saudi Arabia among the contenders because it would bring money and a lucrative market to a project expected to cost tens of billions of dollars.

Other companies involved in the project include European missile maker MBDA, Japanese avionics manufacturer Mitsubishi Electric Corp, and engine makers Rolls-Royce PLC, IHI Corp and Avio Aero.