According to a statement released by the Abu Bakr al-Siddiq Battalion, Seif al-Islam Gadhafi was released on Friday, but the group gave no details on his whereabouts citing concerns over his safety.

The Associated Press news agency said Seif al-Islam was apparently released by his captors as part of an amnesty law promulgated by the North African country's parliament based in the east.

"We have decided to liberate Seif al-Islam Gadhafi. He is now free and has left the city of Zintan," the group's statement on Facebook read.

The group made a similar statement in July 2006, but it was later denied by the authorities in Zintan.

Rise and fall of Gadhafi's heir-apparent

Seif al-Islam was captured by the Battalion's fighters late in 2011, the year when a popular uprising toppled his father's 42-year-old government. Mass protests later plunged the oil-rich North African nation into a civil war in which rebels killed Moammar Gadhafi. Three of Gadhafi's seven sons were also murdered in the 2011 uprising.

Read: Seif al-Islam: From Libyan reformer to hardliner

In June 2011, the International Criminal Court (ICC) issued warrants for Seif al-Islam, his father and intelligence chief Abdullah al-Senussi for crimes against humanity in relation to the then administration's brutal measures to suppress the uprising.

Seif al-Islam, 44, and eight other Gadhafi-era officials were sentenced to death by a Tripoli court in 2005.

Turmoil in Libya

Since the overthrow of Moammar Gadhafi's government in 2011, Libya has plunged into a civil war with rival groups setting up two governments and two parliaments. Each is backed by heavily armed former rebels. The authorities in the east do not recognize the UN-backed Government of National Accord (GNA) based in the capital, Tripoli.

Post-Gadhafi rulers have struggled to impose order with much of the country paralyzed by political infighting and armed conflicts.

A London School of Economics alumnus, Seif al-Islam was once a progressive face of his father's dictatorial regime and made repeated attempts to improve ties with the West.

In June last year, Seif al-Islam's lawyers said they would ask the ICC to dismiss the case against him.

"The reality is that a trial has taken place. He has been tried and convicted in Libya. It is a clear principle of law that one cannot be tried twice for the same offence," defense laywer Karim Khan told the Hague-based ICC.

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shs/jlw (AP, AFP)