By Marie-Louise Gumuchian and Ali Shuaib
TRIPOLI (Reuters) - Plagued by violence, drugs, weapons trafficking and an influx of illegal immigrants, Libya's new rulers are seeking to clamp down on lawlessness in the vast desert south by closing the region's porous borders.
Since the end of the war that ousted dictator Muammar Gaddafi last year, Libya's southern regions have struggled with smuggling, lingering unrest and insecurity.
Aiming to soothe local discontent over Tripoli's perceived inaction in countering the chaos, the General National Congress on Sunday ordered the temporary closure of Libya's borders with Chad, Niger, Sudan and Algeria.
Days after Prime Minister Ali Zeidan concluded a regional tour to those countries, the national assembly also declared seven southern areas restricted military areas.
While the decree may allay regional worries over Libya's lingering insecurity, the lack of a strong army or border force raises questions of what effect it will have on the ground.
"The aim is to improve security, stem the smuggling of weapons, illegal immigration," a congressman, who did not want to be named due to the sensitivity of the matter, told Reuters.
"How the decree is implemented is for the government and army chief to see. At least we are taking steps."
In the south, where tribal ties are more powerful than on the Mediterranean coast, porous borders, discontent and the availability of arms make the region one of the biggest potential problems for the government.
Weak security forces have exercised little control as tribal battles over power and lucrative trade routes have exacerbated instability.
Earlier this month, several southern congress members boycotted sessions in protest, citing increased violence by armed groups there as well as drug trafficking - just as around 200 prisoners escaped from a jail in the desert city of Sabha.
Much of Libya's southern border is guarded by autonomous local brigades. In the absence of an effective national army, the state often relies on former rebel fighters for security.
"The degree to which borders are actually sealed will depend on the degree to which it has incorporated the different militias that operate along those borders and the degree to which it will try to formalize their control over those borders," Geoff Porter, of North Africa Risk Consulting, said.
Restoring order in the south is important to the stability of the wider region, where concerns over Libya's precarious security have been exacerbated by the resurgent threat of Islamist militancy stemming from northern Mali.
In the chaos since Gaddafi's fall, the south has become a smuggling route for weapons which have reached al Qaeda militants deeper in the Sahara.
It is also used for trafficking legal and contraband goods. In Niger's Agadez region, a transit point to Sabha, Tuareg and Tibu gunmen clash regularly to slough off ill-gotten gains in Libya, including vehicles and weapons, a security source said.
The decree allows the defense ministry to appoint a military governor with the authority to arrest fugitives from justice and deport illegal immigrants.
"It is a huge job and depends if the army has the force to do it," an official in Sabha said. Little details have been given about how security forces will go about the plan. Col Ali al-Amari said a border force would be integrated into the army.
Zeidan has said agreement was made in principle with the countries he visited to secure Libya's borders.
"Libya is worried about Gaddafi supporters outside, especially since the deterioration of the situation in Mali," Anis Rahmani, security expert and editor of Algeria's Ennahar daily, said. "Coordination between Algeria and Libya is good."
Niger, where Gaddafi's son Saadi fled to last year, welcomed the decision provided the authorities could implement it well.
"What we want is that the Libyan authorities have the capacity to ensure that this measure is effectively implemented and that we benefit from the expected effects," Foreign Minister Mohamed Bazoum told Reuters.
"Since February 2011, the border had become very porous and very conducive to trafficking and crimes which have a very negative impact on our region and the security of the Sahel-Saharan region."
In Khartoum, Foreign Ministry spokesman El-Obeid Morawah said: "Libya's step was not a surprise to us. There was total mutual coordination."
"Sudan is harmed by the leakage of arms from remnants of Gaddafi's regime across the border to rebel movements in Sudan."
Libyan congressman Hassan al-Amine said such a decree should have come sooner. "We hope this will secure the south," he said.
(Additional reporting by Abdoulaye Massalatchi in Niamey; Khalid Abdelaziz in Khartoum and Lamine Chikhi in Algiers; Writing by Marie-Louise Gumuchian; Editing by Michael Roddy)