TRIPOLI, Libya — Libya on Thursday barred Italy, one of the country's largest investors, from its oil sector because of Rome's role in the NATO airstrikes on the country, a move that raised serious questions about investments by Italian oil giant ENI SpA in the OPEC member state.

The North African nation's prime minister left the door open for other alliance nations to re-evaluate their roles in the strikes or risk facing the same fate, in a possible attempt to fracture the wavering commitment by some to the campaign.

"The Italian government needs to totally forget about Libyan oil and every agreement we signed in the past," Al-Baghdadi al-Mahmoudi told reporters in the Libyan capital. "ENI will have to look elsewhere for business."

NATO has been striking forces loyal to Libyan leader Moammar Gadhafi and regime-linked military sites under a U.N. resolution aimed at protecting civilians. On Wednesday it reported carrying out 50 strikes, including missile launchers near Tripoli.

But the civil war pitting the Tripoli government against rebel fighters has hit a virtual stalemate, with neither side able to make significant advances over the past few weeks.

Libyan officials have warned nations involved in the NATO campaign that they could be barred from investing or participating in the country's oil sector if they continue to side with the rebels. But Italy — Libya's former colonial master — appears to be the first country to be formally barred.

"Now is the last chance for anyone contributing to the aggression against our nation to review their position as fast they can so they have a chance in the future for oil dealings with Libya," said al-Mahmoudi.

He said Libya was already in negotiations with Russian, Chinese and even American companies for future oil deals. He said Italy was specifically targeted because of Italian Prime Minister Silvio Berlusconi's once-close relationship with the North African nation and a friendship pact signed by the two nations.

"To add insult to injury, Berlusconi says he never agreed to the aggression and was pushed to participate," said al-Mahmoudi, referring to Berlusconi's July 7 comments that the Italian parliament forced his hand.

"Well, if he says he was pressured to attack Libya, then I was pressured by the Libyan people to cut ties with Italy," al-Mahmoudi said.

Italy's position is that the treaty is "suspended" as a result of the Libyan regime's attacks on its own population.

Libya sits atop Africa's largest proven reserves of conventional crude. But months of fighting between pro-Gadhafi forces and the rebels have essentially halted what was once about 1.6 million barrels per day of oil output — a drop that helped propel crude prices well beyond $100 per barrel earlier in the year.

In the years since Libya re-emerged from more than a decade of international isolation for Tripoli's support of terrorism, Western oil giants rushed to tap into the country's reserves, with ENI among the most active in the country.

But the outbreak of fighting in February led to new international sanctions that targeted, among other things, Libya's oil sector. International companies have largely pulled out their foreign workers and fields are idling well below their production capacity because of the exodus of workers.

"Those who come one step toward us, we will come two steps toward them," al-Mahmoudi said. "But Italy is finished."

Despite the U.S.'s leading role in the attacks and Secretary of State Hillary Clinton's recent remarks that Gadhafi's days were numbered, the prime minister specifically left the door open to U.S. companies because its role in the campaign is largely restricted to logistics.

"(America) reviewed its position and its participation has been much weaker and this helps the U.S. with its relationship with Libya," al-Mahmoudi said. "That's why were are prepared to work with the U.S. in the oil industry."