BRUSSELS (Reuters) - EU antitrust regulators have extended their review of the proposed $28 billion merger between of Deutsche Boerse <DB1Gn.DE> and the London Stock Exchange <LSE.L> by three weeks after the exchanges asked for more time.

The European Commission delayed its decision on the deal by 15 working days to March 6, 2017, from Feb. 13.

"We extended the deadline at the request of the parties," Commission spokesman Ricardo Cardoso said in an email.

The EU antitrust authority last month warned the companies that their deal may hurt competition in a broad range of financial market activities. [nL8N1C43XX]

LSE plans to hive off the French half of its LCH.Clearnet arm in a bid to ease EU concerns about the deal although the companies have not formally submitted any concessions to the Commission.

Pan-European bourse Euronext <ENX.PA>, which opposes the Deutsche Boerse merger with the LSE, said this week it was the "natural buyer" for Clearnet, but not at any price. [nL8N1CO43P]

Deutsche Boerse had no comment and LSE had no immediate comment on the extension.

(Reporting by Foo Yun Chee and Huw Jones; editing by Philip Blenkinsop and Jason Neely)