Renzi was speaking on a TV talk show on the day that two Italian hostages freed in Libya after two fellow captives were allegedly killed by Islamic State militants were flown back home.

"As long as I am prime minister, Italy will not go to Libya for an invasion with 5,000 men," Renzi told Canale 5 television.

He was responding to the U.S. ambassador to Italy, John Phillips, who told the Corriere della Sera daily on Friday that Rome could send up to 5,000 troops, adding: "We need to make Tripoli safe and ensure that ISIS is no longer free to strike."

Rome is working with other Western powers and the United Nations to try to convince two rival Libyan governments to create a single, unity coalition and focus their energy on the fight against Islamic State.

In the meantime, the Americans have launched air strikes on Islamic State outposts in the country and the French have conducted surveillance flights. U.S., French and British special forces are also in the country, officials and media have said.

Italian officials have said Italy sent some 40 secret service agents to Libya in recent weeks, with an additional 50 special forces operatives set to join them.

Rome however is resisting pressure to allow aircraft and armed drones to stage attacks on Islamic State militants in Libya from its territory. It is also trying to persuade its allies to limit action until a government is in place and requests international help.

"If there is a need to intervene, Italy will not back down. But this is not the situation today. The idea of sending 5,000 men is not on the table," Renzi said.

The two freed hostages and their slain companions were employees of Italian construction company Bonatti. They had all been seized last July near the western Libyan city of Sabratha.

Gino Pollicardo and Filippo Calcagno arrived at Rome's military airport of Ciampino on Sunday. According to a spokesman for Libyan security forces in Sabratha, Sabri Kshada, the pair were released during a raid early on Friday.

Fellow captives Salvatore Failla and Fausto Piano were shot dead by Islamic State militants shortly before Libyan forces attacked on Wednesday, Kshada has said. However the exact circumstances of both the killings and the release remain unclear.

Sabratha is one of several Libyan cities in which militants loyal to Islamic State have established a presence, taking advantage of the chaos since Muammar Gaddafi was toppled in an uprising five years ago.

Before departing for Italy from Tripoli's Mitiga arport, Pollicardo and Calcagno briefly appeared beside Ali Abu Zakouk, the foreign minister of Tripoli's self-declared government.

"We need support and cooperation from the Italians to tackle the criminal organisation of Islamic State in Libya," Zakouk said.