EU regulators on Friday opened an anti-trust probe into the planned $6.3 billion buyout of US office supplies giant Office Depot by American rival Staples.

"The European Commission has opened an in-depth investigation under the EU Merger Regulation into the acquisition of office supplies distributor Office Depot by its competitor Staples," the bloc's executive arm said in a statement.

"The Commission has concerns that the takeover could lead to price increases and less choice," it added.