Western allies are set to launch airstrikes against an Islamic State stronghold in Libya, the country's ambassador to the United Nations told Italian newspaper La Stampa on Thursday.

Ibrahim Dabbashi spoke in reaction to the overnight approval of a UN Security Council resolution urging the formation of a Libyan national unity government within 30 days and world powers to help the new administration defeat Islamist terrorism.

"Italy, France, Britain and the United States are preparing air raids to hit Islamic State bases in Sirte. I think they will enter into action as soon as political conditions will allow," the ambassador said.

Dabbashi said Libyan forces would conduct the ground fight against the Islamists, but added that "the government will need air support."

The Council gave its backing Wednesday to the new national unity government in embattled Libya, a move it hopes will help stem mass migration to Europe and reverse gains made by jihadists from the Islamic State group.

The 15-nation council gave its support to the deal signed last week in the Moroccan town of Skhirat between representatives of strife-torn Libya's two competing regimes.

Britain's ambassador to the United Nations, Matthew Rycroft, presented the motion, which he said represents a "strong collective sign of our commitment to Libya's sovereignty, territorial integrity and national unity."

"This is just the start of a process to deliver a prosperous and stable future for all Libyans," Rycroft declared. "We urge all those who have not yet signed to decide now to support the agreement and to work with the government of national accord."

The United Nations envoy to Libya, Martin Kobler, is now working on arrangements to allow the unity government to safely set up shop in Tripoli, which is under the control of militia fighters.

"I encourage those who are not yet on board to join - the door is wide open," said Kobler after the UN vote, adding that a top priority of the new unified government will be "the fight against Daesh, the threat of Daesh" which he said is expanding toward the east, west and south of Libya.

Kobler employed the Arabic acronym used by many to refer to the jihadist Islamic State group, also known by the acronyms "ISIL" and "ISIS."

Libya has been in chaos since the 2011 uprising that toppled dictator Moammar Gadhafi, with armed factions battling for territory and control of its oil wealth.

bik/rc (AFP, dpa, Reuters)