Libya's ruling national congress has ordered the temporary closure of its borders with four of its neighbours and declared its vast desert south a closed military zone in the face of growing unrest and immigration.

The national assembly ordered the "temporary closure of the land borders with Chad, Niger, Sudan and Algeria pending new regulations", a decree carried by the official LANA news agency said.

It added that the provinces of Ghadames, Ghat, Obari, al-Shati, Sabha, Murzuq and Kufra "are considered as closed military zones".

The decree also gave the defence ministry powers to appoint a military governor, from outside the area, with authority to arrest fugitives from justice and deport illegal immigrants.

Prime Minister Ali Zeidan returned from a regional tour last week, during which he called for a meeting in Libya with Niger, Mali, Chad and Sudan to secure regional borders.

Several southern members of the congress have boycotted sessions recently in protest against lawlessness plaguing the south, citing increased violence by armed groups there as well as drug trafficking.

"This decision shows that the congress understands the situation in the south, where the security is bad," Mohamed Menawi Al-Houdhiery, a congress member from Sabha, told Reuters.

Earlier this month, nearly 200 prisoners escaped from a jail in Sabha, which has also seen tribal clashes since the end of last year's war that ousted Muammar Gaddafi.

Restoring order in the south is not only important internally for Libya but also for stability in the wider region.

In the chaos that followed Gaddafi's fall, the south was used as a smuggling route for weapons reaching al Qaeda in the Sahara.