Gunmen on Sunday killed a former security officer who served under slain dictator Moammar Gadhafi in the violence-ridden eastern city of Benghazi, security and medical sources said.

"Retired colonel Muftah Najem was shot dead," said a spokeswoman for Al-Jala hospital where the body was taken.

Libya and Algeria agreed Sunday to boost cooperation on border security, illegal immigration, weapons trafficking and "terrorism,” during a visit by Algerian Prime Minister Abdelmalek Sellal.

His trip to Tripoli, which follows a January summit in Ghadames between Algeria, Libya and Tunisia, was marred by protests demanding Libyan Prime Minister Ali Zeidan's resignation.

Four U.S. military personnel have been released after being detained briefly by the Libyan government, the U.S. State Department said on Saturday.

State Department spokeswoman Jen Psaki, who hours earlier had announced the Americans' detention, did not say why they were held, though the New York Times reported that the incident unfolded following a confrontation at a checkpoint where gunshots were fired.

Four U.S. military personnel have been freed after a brief detention by the Libyan government, the U.S. State Department said Saturday.

State Department spokesperson Jen Psaki, who hours earlier announced that the Americans had been detained, did not say why they were held.

Dozens of demonstrators gathered in central Tripoli on Friday to protest against Libya's General National Congress extending its mandate until the end of 2014.

An Agence France Presse correspondent said the protesters gathered in Martyrs Square to chant slogans against Monday's move.

Two Libyan army officers have been killed in the past 48 hours in the eastern city of Benghazi, cradle of the 2011 revolt against Moammar Gadhafi, officials and medics said.

The restive east has seen frequent attacks on security forces as the weak government in Tripoli has struggled to exert control over former rebels who have refused to disarm or join the security forces.

Moroccan authorities said Thursday they had dismantled a "terrorist cell" operating in several cities that included people trained in the use of firearms and explosives.

North Africa has been on heightened alert in recent years as regional jihadist groups have grown more powerful and as the turmoil in Libya following Moammarr Gadhafi's 2011 overthrow has left the vast and mostly desert region awash with weapons.

Libyan Prime Minister Ali Zeidan expressed hope on Wednesday that last-ditch mediation can end a crisis sparked by the months-long blockade of eastern oil terminals by striking security guards.

"Delegations whose tribes have their own initiatives have decided to engage in mediation to find a solution to the crisis," Zeidan told reporters.

A Libyan soldier was shot dead and a civilian wounded by a bomb under his car in separate attacks in the eastern city of Benghazi on Tuesday, medics and security sources said.

"A soldier from the Libyan army was killed and a civilian was seriously wounded," a security source said.

Libya's General National Congress, the country's highest political authority, extended its mandate Monday until the end of next year, a GNC spokesman said.

The GNC had accepted the "principle... to fix the end of the mandate for December 24, 2014 to hand over power to another legislative body," Omar Hmeidan said.