By Michelle Nichols

UNITED NATIONS, June 3 (Reuters) - Work on a United Nations Security Council resolution authorizing a European Union naval mission to stem the deadly flow of migrants across the Mediterranean has been put on hold until Libya consents to the operation, diplomats said on Wednesday.

The 28-nation bloc wants to capture smugglers and dismantle their boats to help it tackle the rising number of migrants fleeing war and poverty in Africa and the Middle East. But it needs Libyan consent and also wants U.N. authorization to allow it to operate in Libyan territorial waters and coastal areas.

European members of the 15-member Security Council - Britain, France, Lithuania and Spain - have been drafting a resolution to approve the operation under Chapter 7 of the U.N. Charter, which allows the use of force.

A senior U.N. diplomat said drafting of the resolution had been "paused" until it was "clear there will be Libyan consent."

"It's a crucial requirement for the resolution as currently configured and the mission as currently envisaged," he said, speaking on condition of anonymity, adding that the Europeans were not seeking to push through a resolution given concerns over sovereignty.

"(It's) a process that's turning out to be longer than expected; nevertheless, a constructive process," he said.

A second senior U.N. diplomat confirmed that work on the resolution put on hold.

Libya has descended into chaos nearly four years after the fall of Muammar Gaddafi. Two competing governments backed by militias are scrambling for control of the oil-producing country.

The first senior diplomat said that legally a letter from a representative of the internationally-recognized Libyan government was needed to authorize the EU mission, but that to ensure successful implementation of the operation "cooperation with a wide variety of authorities" would also be required.

The European Union is trying to achieve this without disrupting U.N.-led talks aimed at forming a unity government to end the power struggle between the rival administrations. The diplomat said the European Union hoped to gain Libyan consent for the operation before the formation of a unity government.

Libyan politicians and activists resumed talks on a unity government on Wednesday.

Russia, a U.N. Security Council permanent member with veto power, said on Monday that any resolution must precisely define the powers of an EU naval mission to win Moscow's backing.

Some 1,800 migrants have perished in the Mediterranean this year, the U.N. refugee agency has said, while tens of thousands more have made it to Europe. (Reporting by Michelle Nichols, editing by G Crosse)