Security services on Monday stepped up efforts to locate two Serbian embassy staffers kidnapped the previous day in the Libyan coastal city of Sabratha, an Islamist stronghold.

"The investigation goes on. The state of alert raised on Sunday is still in place. We are actively searching for the two kidnapped Serbs," said an official of Sabratha's military council in charge of security.

"We've found a car which could belong to the kidnappers and we are still questioning the Libyan chauffeur of the two Serbs," he told AFP, speaking on condition of anonymity.

The foreign ministry in Belgrade said the two embassy employees, a man and a woman, were snatched in Sabratha, 70 kilometres (42 miles) west of Tripoli, from a convoy of cars headed to the Tunisian border.

The pair were named as Sladjana Stankovic, in charge of communications, and her embassy driver, Jovica Stepic.

Serbian Foreign Minister Ivica Dacic has said Belgrade had "no information" about the identity of the kidnappers.

Serbia's ambassador Oliver Potezica who witnessed the incident told Serbian media that masked assailants had "provoked an accident, hitting one of the embassy cars from the back" to carry out the abductions.

One attacker had opened fire on a Libyan national in the convoy and hit him in the leg.

Sabratha's municipal council, on its Facebook page, criticised the Serbian ambassador for having failed to give advance notice to local authorities of their travel plans.

This had allowed the kidnapping to take place, it said, adding that the council did not have any information on the kidnapped pair's state of health or where they were being held.

In contrast, "once local authorities had been informed... security was provided to escort the Serbian ambassador and his delegation safely" to the border crossing with Tunisia, it said.

Libya descended into chaos after the October 2011 ouster and killing of longtime dictator Moamer Kadhafi, with two governments vying for power and armed groups battling to control its vast energy resources.

A militia alliance including Islamists overran Tripoli in August 2014, establishing a rival government and parliament that forced the internationally recognised administration to flee to the country's remote east.

Belgrade maintains an embassy in Tripoli and Serbian citizens, mostly doctors and other medical staff as well as construction workers, have been working in Libya for decades due to close bilateral relations during Kadhafi's regime.

Sabratha is on the edge of a region known as Jefara, which analysts say is home to formerly nomadic tribes that make a living from smuggling and trafficking.

In June, after a Tunisian student armed with an assault rifle mowed down 38 tourists at a beach resort in his country, Tunisia's secretary of state for security said the shooter had been trained in Sabratha.