BRUSSELS/MILAN - Vodafone and Telecom Italia (TIM) have offered concessions in an effort to allay EU antitrust concerns over their plan to create Italy's biggest mobile towers company, a filing on the European Commission website showed on Monday.

Under the deal announced in July last year, Vodafone will transfer its Italian mobile masts to INWIT, which is 60% owned by TIM.

With EU antitrust regulators taking a tough line on telecoms mergers that reduce the number of players in a market from four to three, the sector is hoping that deals where operators combine towers or share networks will make it easier for them to reduce debt and share costs.

The companies submitted their offer on Friday and the EU competition enforcer on Monday extended its deadline for a decision on the deal to March 6 from Feb. 21.

The Commission will now seek feedback from the companies' rivals and from consumers before deciding whether to accept the offer, demand further measures or open a full-scale investigation.

Mobile virtual network operators (MVNOs) in Italy want the companies to provide access to their network once the deal is completed, especially as they roll out 5G infrastructure, sources close to the matter told Reuters. MVNOs offer mobile services to their customers over the wireless network infrastructure of bigger rivals.

Reuters reported on Feb. 13 about the Commission's demand for concessions.

Vodafone and TIM had no immediate comment.

TIM shares were up 0.4% up in morning trade while Vodafone was flat.

(Reporting by Foo Yun Chee Editing by David Goodman ) ((foo.yunchee@thomsonreuters.com; +32 2 287 6844; Reuters Messaging: foo.yunchee.thomsonreuters.com@reuters.net))