Libya's UN-backed government has sent NATO an official request to help improve its security and defences, the alliance said Thursday.

NATO agreed at a summit last year in Warsaw to offer support, if requested, to the Government of National Accord, which it wants as a bulwark against migrant flows and terrorism.

"Last night, I received a formal request from Libyan Prime Minister Fayez al-Sarraj requesting NATO's advice and expertise in the field of defence and security institution building," NATO chief Jens Stoltenberg told a press conference in Brussels.

The 28-nation transatlantic alliance, which is holding a meeting of its defence ministers, will discuss how to respond to the request as soon as possible, Stoltenberg said.

During talks earlier this month in Brussels with Sarraj, Stoltenberg offered to help Tripoli to build up its navy and coast guard in concert with EU efforts to curb migrant smuggling from the north African country to Europe.

Stoltenberg said NATO could also offer advice to the Tripoli government on establishing a modern ministry of defence, a joint military staff and security and intelligence services under civilian control.

Sarraj's government is locked in a power struggle with a rival administration in eastern Libya as it seeks to end years of lawlessness following the 2011 overthrow of Moamer Kadhafi.

The EU is still waiting for the Libyan government to give permission for its naval operation Sophia to enter the chaos-wracked country's waters to expand on its missions to stop migrant smuggling to Europe.