A local chief of the Islamic State (ISIS) militant group and two aides have been captured in a city near Libya's capital, according to the Tripoli-based government which is not internationally recognised.

The Tripoli interior ministry's special forces unit, on its Facebook page, said the ISIS "emir" for Sabratha, Mohamed Saad al-Tajuri, also known as Abu Sleiman, was seized in the city, 70 kilometres (45 miles) west of the capital.

It did not specify his nationality or those of his two aides.

On Wednesday, ISIS militants killed 18 people in clashes as they briefly occupied the heart of Sabratha before they were ousted by militia fighters, according to officials in Tripoli.

A US air strike near Sabratha last week targeted a suspected ISIS training camp, killing 50 people. Serbia said two of its diplomats being held hostage were among the dead.

ISIS has taken advantage of growing chaos to expand its foothold in Libya, which has rival administrations vying for power.

The internationally recognised government fled Tripoli in mid-2014 after the Fajr Libya militia alliance overran the capital and set up its own parliament.

Last June, ISIS seized the coastal city of Sirte, east of Tripoli, raising fears that it is establishing a new stronghold on Europe's doorstep.

The group has since attacked key coastal oil facilities and staged a string of suicide bombings.A local chief of the Islamic State (ISIS) militant group and two aides have been captured in a city near Libya's capital, according to the Tripoli-based government which is not internationally recognised.

The Tripoli interior ministry's special forces unit, on its Facebook page, said the ISIS "emir" for Sabratha, Mohamed Saad al-Tajuri, also known as Abu Sleiman, was seized in the city, 70 kilometres (45 miles) west of the capital.

It did not specify his nationality or those of his two aides.

On Wednesday, ISIS militants killed 18 people in clashes as they briefly occupied the heart of Sabratha before they were ousted by militia fighters, according to officials in Tripoli.

A US air strike near Sabratha last week targeted a suspected IS training camp, killing 50 people. Serbia said two of its diplomats being held hostage were among the dead.

ISIS has taken advantage of growing chaos to expand its foothold in Libya, which has rival administrations vying for power.

The internationally recognised government fled Tripoli in mid-2014 after the Fajr Libya militia alliance overran the capital and set up its own parliament.

Last June, ISIS seized the coastal city of Sirte, east of Tripoli, raising fears that it is establishing a new stronghold on Europe's doorstep.

The group has since attacked key coastal oil facilities and staged a string of suicide bombings.