Glencore has formally notified the European Commission of its $33 billion plan to take over Xstrata, sources familiar with the matter told Reuters on Tuesday, setting the European regulatory clock ticking on the deal.

Once the notification has been acknowledged by the Commission, the regulator has 25 days to decide whether to approve, reject or begin an in-depth probe into a plan to create the world's fourth largest miner.

The European Commission is not the final anti-trust hurdle for the two companies who also still need approval from China's Ministry of Commerce (MOSCOM), the newest of the world's heavyweight regulatory bodies.

The sources did not give any further details on potential remedial sales which may or may not have been proposed.

Xstrata and Glencore declined to comment.