Italy says it will only recognise Libya's anti-Gaddafi Transitional National Council (TNC) in talks about the north African country's future.
Foreign Minister Franco Frattini said the recognition would be "formal... as France and Qatar have already done".
Italy has been cutting its previously close ties with the government of Colonel Muammar Gaddafi.
Mr Frattini said proposals from a Gaddafi envoy to end the Libyan crisis were "not credible".
The TNC's foreign minister, Ali al-Essawi, rejected the idea of a transitional government in Libya headed by one of Col Gaddafi's sons.
He also thanked Italy for its "support for the revolution".
Mr Frattini accused the Gaddafi government of using illegal immigration as a "weapon" in the conflict.
His comments were made as Prime Minister Silvio Berlusconi visited Tunisia to discuss how to halt a flow of migrants.
Thousands of people, mainly from Tunisia, but also from Libya and Egypt, have arrived on the tiny Italian island of Lampedusa in recent weeks, overwhelming the local population.
Emigration controls that used to be enforced by both Tunisia and Libya have largely lapsed since the eruption of civil unrest.
Mr Berlusconi said he wanted Tunisia to crack down on emigration again.
"We are in a friendly country to resolve the problem of migrants. The climate of friendship, collaboration and co-operation is good," he said as he arrived for talks with the prime minister and president.
Mr Berlusconi's trip to Tunisia meant he was missing his latest scheduled court appearance. He is on trial accused of manipulating a business deal to skim off money into a political slush fund - charges he denies.