Troops deployed in Tripoli on Monday after militias were ordered to leave the capital following deadly weekend clashes sparked by a protest against the former rebels in Libya's 2011 revolt.
The unrest was the deadliest in the capital since the uprising and erupted when the former rebels from Misrata opened fire on protesters, triggering the clashes that killed at least 43 people and wounded 450.
As the capital began observing a three-day period of mourning on Sunday, gunmen seized the deputy head of Libya's intelligence services Mustafa Nuh near Tripoli airport.
But his abductors released him on Monday, an intelligence official told AFP.
"Nuh has been freed today (Monday)," the source said on condition of anonymity, without elaborating.
The abduction of Nuh, who is himself originally from Misrata, came amid persistent tensions between armed groups from his hometown and rivals in Tripoli.
Community leaders, officials and former rebel commanders from Misrata urged the "withdrawal of all ex-rebels from the city of Misrata who are in Tripoli, whatever their group is ... in under 72 hours," in a statement issued late Sunday.
More from GlobalPost: Tripoli: Friday's deadly protest a prelude?
In the streets of the capital itself, dozens of soldiers and armored vehicles deployed on Monday in response to the violence.
"A number of units of the national army are about to enter the city of Tripoli from several areas in order to secure it," the government said in a statement.
In the same statement, the defence ministry urged residents of the capital to give all necessary help to the troops to allow them to carry out their mission.
Soldiers perched on armored vehicles were seen making their way to the city centre from the east, making victory signs at passing drivers, who honked their horns in approval.
The Misrata brigade at the heart of the latest violence saw some of the heaviest fighting during the uprising against Kadhafi, when Misrata was besieged by regime forces.
While such groups were initially hailed as heroes for their role in toppling the Kadhafi regime in 2011, public frustration with militias has been growing.
Many groups have rejected government calls to lay down their arms or integrate into the armed forces, instead carving out their own fiefdoms across the vast mostly-desert country.
Demonstrators protesting against militias on Friday in Tripoli's Gharghour neighborhood were fired upon from villas occupied by the fighters from Misrata, who killed several protesters before rival militias swept in, sparking clashes that continued until Saturday.
In response to the bloodshed, Tripoli's city council had called a three-day general strike, and on Monday many shops and businesses were closed around the capital, an AFP journalist said.
Universities in Tripoli on Monday announced they would close for the week.
Hanan Salah, a researcher with Human Rights Watch, said the latest clashes "showcase the extent of the reckless acts of unaccountable militias these past two years, and the government's lack of ability to control them".
Elsewhere, a senior military officer escaped a bomb blast on Monday in the eastern city of Benghazi, which has been the scene of regular violence since 2011.
The city's military governor escaped an assassination attempt that killed a member of his entourage and seriously wounded another, a security official said.
"The motorcade of Colonel Abdallah al-Saati, head of the joint security room and military governor of Benghazi, was attacked as he passed through the Al-Hadeq area, leaving one dead and one seriously wounded from his entourage," said security forces spokesman Colonel Abdallah al-Zaidi.
Zaidi said that explosives experts were combing the area for to find out how the attack took place.
Bombings and shootings in the region have killed more than 100 army and police officers and judge.