The companies announced a plan last July to create Italy's largest mobile towers group through the transfer of Vodafone's Italian mobile masts to INWIT, TIM's 60%-owned subsidiary.

Once the 10 billion euro ($10.8 billion) merger is completed, TIM and Vodafone would each have a 37.5% stake and equal governance rights in the enlarged INWIT.

The deal includes a network sharing agreement and a partnership to roll out 5G infrastructure jointly across Italy.

For the telecoms industry, combining towers or sharing networks to reduce debt and share costs are seen as alternatives to counter EU antitrust regulators' tough line on mergers that reduce the number of players in a market.

Under Vodafone and TIM's proposal, INWIT would make available around 630 sites each year in towns with more than 35,000 people, allowing rivals to provide current and future mobile and fixed telephony services, said the internal EU paper.

The number of sites available will gradually decrease to just below 400 per year during the fifth year of the companies' proposal, which would be valid for eight years.

The number of sites freed up for rivals over the eight-year period totals 4,000.

TIM and Telecom Italia both declined to comment.

The companies submitted their offer on Friday. The EU competition enforcer extended on Monday 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.

(Reporting by Foo Yun Chee; Additional reporting by Elvira Pollina in MILAN; Editing by Gabriela Baczynska and Jan Harvey)

By Foo Yun Chee