In response to a request from Japan, the 15-nation European Union and Canada, the World Trade Organization will mediate in their dispute over how Ottawa should specifically correct its controversial auto-trade policy, government sources said Sunday.

The WTO's mediation will be aimed at preventing a possible tit-for-tat trade war -- with Japan and the EU on one side and Canada on the other -- after the expiration of the mid-September deadline for Ottawa to rectify its auto policy, the sources said.

It was not immediately known, however, how long the mediation efforts by the WTO -- the Geneva-based watchdog on international commerce -- will last.