MILAN (Reuters) -KKR-backed telecom network firm FiberCop has filed a complaint with the European Commission, alleging that Italy provided state aid to rival Open Fiber in breach of EU competition rules, three sources with knowledge of the matter said.

The complaint, which alleges Italy altered competition in its ultra-broadband market, escalates a standoff between KKR and the Rome government, which is the U.S. fund's co-shareholder in Fibercop.

In an e-mailed statement to Reuters, FiberCop confirmed it had filed a complaint with the EU, without providing details.

"FiberCop brought to the attention of the European Commission a number of circumstances it believes warrant scrutiny from a competition standpoint."

Italy's Treasury, KKR and Open Fiber all declined to comment. The EU Commission did not immediately respond to a request for comment.

KKR owns 37.5% of FiberCop, which manages Italy's main telecom network, while the government has a 16% stake.

FiberCop's complaint, filed on Monday, targets a series of measures Italy adopted in 2024-2025 in relation to Open Fiber, the people told Reuters, asking not to be named as the matter is confidential.

FiberCop estimated in its complaint the measures could be worth up to 4.5 billion euros ($5.3 billion), the sources said.

The measures include direct grants, the extension of existing concessions, state guarantees on credit lines and the suspension, or reduction, of fines linked to delays in state-sponsored fibre rollout plans, the people said.

FiberCop alleged the measures shifted economic and financial risks from Open Fiber onto the state in breach of EU competition rules and were not notified to the EU, the sources said.

KKR and Italy are at loggerheads over the future of FiberCop, which was sold last year to a KKR-led consortium in a 19 billion euro deal.

The U.S. fund is resisting Italy's push to combine FiberCop with Open Fiber, the smaller rival controlled by state investor CDP and Australian fund Macquarie, sources told Reuters earlier this week.

CDP declined to comment. Macquarie did not immediately respond to a request for comment.

A tie-up between FiberCop and Open Fiber would trigger an additional payment of up to 2.5 billion payment from the KKR-led consortium as part of the network spin-off deal.

Open Fiber, which Italy tasked with rolling out fibre optic cables across the country almost a decade ago, posted a 364 million euro loss last year. It forecasts reaching a positive cash flow in 2028 at the latest.

($1 = 0.8566 euros)

(Editing by Valentina Za)