TRIPOLI - Islamist gunmen have stormed a military arms depot in Libya and a nearby port and seized numerous weapons and army vehicles after killing four soldiers, a security official said on Sunday.

The group also took several hostages, both soldiers and civilians, and is "threatening to execute them unless a siege by security forces is lifted" in Al-Baida, the official said, asking not to be named.

"This criminal gang assaulted an army weapons depot and seized 250 weapons, killed four soldiers and wounded 16 others" in the Wednesday operation in Derna, which lies east of Al-Baida and 1,300 kilometres from Tripoli.

"Army Colonel Adnan al-Nwisri joined them and provided them with a rocket-propelled grenade launcher, three pieces of anti-aircraft artillery and 70 Kalashnikov" assault rifles, the source said.

On Friday, he said they attacked the port in Derna and seized an assortment of 70 military vehicles.

It was not immediately clear who the civilians were or where they had been taken hostage.

The group calls itself the "Islamic Emirate of Barqa," after the ancient name of a region of northwest Libya, and the official said its leadership is made up of former Al-Qaeda fighters previously released from jail.

The official said the same group was responsible for the hanging of two policemen in Al-Baida on Friday that was reported in Oea newspaper.

Justice Minister Mustafa Abdeljalil started negotiations late on Saturday for the hostage-takers to release their captives, he said. "But we will not negotiate over Libya's integrity under any circumstances."

According to Human Rights Watch, at least 23 people have died in Al-Baida since Tuesday in clashes between security forces and protesters against the four-decade rule of Libyan leader Moamer Kadhafi.

Over the past five years, Libya has freed around 850 prisoners from different Islamist groups, 360 of them since March.

Among those released were jihadists with ties to Al-Qaeda's Iraqi and North African franchises, including senior members of the Libyan Islamic Fighting Group (LIFG) such as its chief Abdelhakim Belhaj.

In November 2007, Al-Qaeda number two Ayman al-Zawahiri allegedly said the LIFG had joined his network, in an unverified audio recording posted online.

But the Kadhafi Foundation headed by Seif al-Islam, son of Kadhafi, said in 2008 that Islamists held in Libyan prisons and previously linked to Al-Qaeda had renounced their ties.

LIFG was formed in the early 1990s in Afghanistan by Libyan militants who took up arms against Soviet occupation forces. Its stated aim is to overthrow Kadhafi's regime and establish an Islamic state.

The group was led from central Asia by Abu Laith al-Libi, a top lieutenant of Al-Qaeda leader Osama bin Laden, until his killing in February 2008 in a US missile attack in Pakistan.

In March 2006, Libya released 84 jailed members of the country's banned Muslim Brotherhood movement held since the late 1990s.

Fifty-five of those freed returned to Benghazi, Libya's second largest city and reputed opposition stronghold that has been the scene of some of the deadliest anti-regime clashes over the past week.

In 1998, Libya arrested 152 Brotherhood members. In 2002, two members were sentenced to death, 73 to life in prison and 66 were acquitted, while the others were handed 10-year jail terms.

Those condemned, mainly students and academics, were accused of supporting or belonging to Al-Jamaa al-Islamiya al-Libiya, an Islamist group whose beliefs mirror those of Egypt's Muslim Brotherhood.

The offenders are generally charged with violating Libya's Law 71, which bans political activity opposed to the principles of the 1969 revolution in which Kadhafi took power.

Evicting Libya's monarchy, Kadhafi has since ruled the country with an iron fist, imposing an ideology inspired by socialism and Islam that he presents as the ultimate evolution of democracy and is enshrined in his "Green Book."