Libyan rebels fighting to overthrow Muammar Gaddafi have won recognition as the country's "legitimate authority" from the entire international contact group co-ordinating policy on the crisis.
Franco Frattini, Italy's foreign minister, announced the largely symbolic move at an Istanbul meeting of the group – one of a swath of political and economic measures designed to ratchet up pressure on Gaddafi.
Britain also announced it was deploying four more fighter aircraft to take part in Nato's bombing campaign.
"The entire Libyan contact group decided to recognise the NTC [national transitional council] as the legitimate authority of Libya," Frattini told reporters. "So [there is] no other option but for Gaddafi to leave."
The recognition will be officially announced when the meeting's final document is released later on Friday.
Diplomats billed the move as a boost to the Benghazi-based rebel council, though it is legally complex since most contact group countries still maintain diplomatic relations with the Gaddafi regime and have embassies in Tripoli and Libyan missions in their own capitals.
Britain has said for some time it regards the NTC as the legitimate representative of the Libyan people but it recognises states, not governments.
"It's a strong signal of support for the NTC and reflects the growing consensus that it is increasingly competent, is reaching out to Libyan people across the country and reinforces the point that Gaddafi must go," said an Foreign Office spokesman.
For some countries the decision may have legal implications with regard to making Libyan state assets frozen by UN sanctions available to the NTC.
The UN envoy on Libya, Abdul-Elah al-Khatib of Jordan, is to be authorised to present terms for Gaddafi to leave power in a Turkish-drafted package that will include a ceasefire to halt fighting and usher in a political transition. It is unclear whether Gaddafi will be required to leave the country. The Libyan leader, wanted for crimes against humanity by the international criminal court, has repeatedly insisted he will not stand down.
The contact group, meeting for the fourth time since the crisis began in March, is made up of more than 30 governments and international and regional organisations, including Nato, the EU and the Arab League.