Libya's ex-rebels reluctant to down arms
More than two months after the death of Col Muammar Gaddafi - and nearly five since he was removed from power - Libya's new government faces problems in securing order.
Tripoli's international airport is now a bustling little place. It is scruffy and in need of a make-over but it is a vital lifeline for Libya as it reopens for business.
Roaming the terminal floor and patrolling the runways are soldiers for whom this is their power-base.
They are ex-rebels from the town of Zintan, south-west of the capital, who captured the airport a few months ago.
'Guardians of revolution'
The uprising that toppled Muammar Gaddafi last year may be over but the Zintanis remain in place: one of the many militias, or 'thwar', that control key areas of the country but are under growing pressure to disband.
But the 'thwar' see themselves as guardians of the revolution. They hail from across Libya. Many of the towns are tiny - Zintan has only around 50,000 inhabitants - but if they happened to win a key victory in the uprising, they took on a significance far beyond their stature in the new Libyan hierarchy.
It was the Zintanis who captured Saif al-Islam Gaddafi back in November. That, along with their control of Tripoli airport, makes them a powerful force.
But as Libya continues its transition from civil war to stable democracy, the government is now trying to rein in the different armed groups, replacing them with a national army and police.
Although the commander-in-chief of the army has recently been named - Youssef Mangoush - the force has yet to be established. The Zintan commander in Tripoli, Mukhtar al-Akhdar, tells me his men will join an army once it's formed, but that for now they have the right to remain in place.
'Duty of protection'
"The martyrs with me sacrificed their blood and souls to defend the revolution", he says.
"We have a duty to protect the airport. The revolution is still in danger. If we leave, there will be problems here. The people who complain about us are jealous because we're doing a good job."
But with sporadic clashes between the groups, the complaints are growing louder.
Demonstrations in Tripoli have called for the brigades from elsewhere to leave the city. In the latest confrontation just a few days ago between militias from Tripoli and Misrata, four men were killed in the heart of the capital.
Mustafa Abdel-Jalil, the chairman of Libya's National Transitional Council, has now warned of the possibility of a "civil war" if the armed groups are not brought under control.
The town of Zawiyah, just west of Tripoli, is leading the way in changing the status quo. A group of ex-rebels there have now formed themselves into a new local military unit, ready to join the national army once it's finally created.
At an old army base, a ceremony formally inaugurates them as military officers: the troops hand over the guns they wielded as militias, applauded by commanders.
They are then given extensive training and taught the discipline that many previously lacked: orderly marching, proper maintenance of their weapons and physical fitness.
They are the first of tens of thousands of former rebel fighters that the government intends to disarm and integrate within new national structures such as the army and police, with many others encouraged to return to civilian life.
Twenty-four year old Abdul Albari is one of those signing up to the army. An engineering graduate and former rebel fighter, he has decided to join the force rather than return to university.
"My country is more important than my studies," he says.
After undergoing a medical check, he's handed his new military uniform. And he tells me the new army can transcend Libya's old divisions.
"I wouldn't mind serving with former pro-Gaddafi fighters as long as they don't have blood on their hands," he says.
"We're all Libyans, all brothers, and the country has a wonderful future."
But that sense of unity is rare, according to Defence Minister Osama Juwali, who believes the lingering resentment between the sides is holding up the formation of a national defence force.
Two armed groups in eastern Libya have already said they will not accept Mr Mangoush as commander-in-chief since he was a colonel under Gaddafi until 1999, when he retired. He then joined the rebels early on in the uprising.
"The main problem is that most of the former rebels have not accepted to work with fighters from the old regime, because they think those people helped Gaddafi during the war," Mr Juwali says.
"The national army and police need time to be formed. And once they're in place, the rebels will hand in their arms, because they'll feel safe."
Almost three months since the country's liberation was formally declared, Libya feels calmer and less volatile than many had predicted. But the continuing presence of the militias is seen as a serious - and growing - threat to stability.
Disarming and persuading them to integrate within national forces is now arguably the greatest challenge facing this fledgling government as it tries to establish security before elections planned later this year.
Col Gaddafi deliberately kept his army weak for fear of a coup, so the new Libya must start afresh. It will be a tough fight.