Leaders of the 12 countries participating in Trans-Pacific Partnership free trade negotiations are expected to hold a summit on Oct. 8, a source involved in the talks said.

The summit, to take place on the sidelines of the Asia-Pacific Economic Cooperation forum leaders' meeting in Bali, Indonesia, is not expected to produce a final agreement but could come up with a basic outline for it, the source said Saturday. It will be held less than three months after Japan joined the U.S.-led initiative in late July.

The TPP participants are trying to conclude what could be the world's most ambitious and comprehensive FTA by the end of this year, more than three years after the talks began in 2010.

Ministers from the 12 who met in Brunei on Thursday and Friday said difficult issues remain in many fields and agreed to maintain "active engagement" in the runup to the summit.

The summit "will be an important milestone as the 12 countries work intensively to conclude this landmark agreement," said a joint statement after the ministerial session.

The source said it is unlikely there will be any further comprehensive negotiating sessions after the Brunei round, and that a lot of the work will be carried out in smaller meetings to address specific sectors.