The Libyan navy said Tuesday it seized an Italian-flagged fishing vessel and is questioning its crew in the western port city of Misrata.

"A coastguard patrol... seized on Tuesday night an Italian fishing boat in (Libyan) territorial waters with seven sailors on board, five Italians and two Tunisians," said Colonel Rida Issa of the marine forces loyal to the UN-recognised Government of National Accord (GNA). 

The boat was steered into the port of Misrata where the seven crew members are being questioned, Issa said at a press conference.

The Italian foreign ministry confirmed the seizure in a statement, adding that the reasons behind it "are not yet clear" but are "likely related to fishing activities". 

The Italian coast is some 300 kilometres from Libya, and there are recurring tensions between Italian and Libyan fishing boats in the area.  

Italian foreign minister Enzo Moavero Milanesi "instructed the Italian ambassador Guiseppe Buccino to work quickly... (to ensure) the correct treatment and rapid release of the crew and boat", according to the statement.  

Libya has been mired in chaos since the ouster and killing of dictator Muammar Gaddhafi in a 2011 NATO-backed uprising.

Two authorities are now vying for power - the GNA based in Tripoli and a parallel administration in the east of the country backed by forces loyal to strongman Khalifa Haftar. 

Hafter launched an offensive to take Tripoli on April 4 and fighting continues south of the capital between Haftar's forces and those of the GNA, including a powerful Misrata militia.