Libya's coastguard said on Thursday it had stopped 280 migrants crammed on five boats, as they attempted the dangerous sea journey across the Mediterranean in a bid to reach Europe.

"A Libyan coastguard patrol boat rescued 280 migrants of various African nationalities," it said in a statement.

The migrants, found on four wooden boats and an inflatable dinghy, were taken to Libya's western port of Zuwara, near the Tunisian border.

They were handed over to the interior ministry for repatriation, it said.

Libya, which plunged into civil war following the 2011 toppling and killing of dictator Moamer Kadhafi, has become a key route for migrants seeking to reach Europe.

The European Union has for several years supported Libyan forces to try to stem migration, despite often grim conditions in the Libyan detention centres where those picked up are sent to.

Rights groups regularly criticise conditions in the centres.

In early October, Libyan authorities arrested some 5,000 mostly African migrants in events that also saw one migrant killed and 15 wounded, according to the UN.

Several days later, guards at a detention centre in the capital Tripoli shot dead six migrants, the International Organization of Migration said, while some 2,000 more escaped.

The UN's migration agency and Libyan authorities on Wednesday repatriated 91 migrants to Niger in a rare humanitarian flight - the second since such trips were suspended two years ago. Many thousands of migrants remain stranded in Libya.

"European states, whose support enables Libyan authorities to prevent people from reaching European shores, should scale up humanitarian evacuations," Human Rights Watch said Wednesday.