Three army and police officers died in separate attacks in Benghazi Sunday, the latest in a string of attacks against security forces in Libya's second city, a security official said.

"Air force Lieutenant Colonel Ali al-Daghani was killed when a device placed in his car exploded near a market," said Abdullah al-Zayedi, a spokesman for the security forces.

Ousted Libyan dictator Moammar Gadhafi's son appeared in court Thursday in Zintan where he is being held by ex-rebels on the same day he was due in Tripoli on security charges.

A lawyer said that Seif al-Islam, charged with undermining state security, appeared in the dock in Zintan west of the capital in a trial that was then adjourned.

Amnesty International Wednesday urged the "immediate" handover of ousted Libyan leader Moammar Gadhafi's son and his intelligence chief to the International Criminal Court, on the eve of a pre-trial hearing in Tripoli.

"The referral of these cases to the Indictment Chamber brings us one step closer to the start of national trial proceedings... in violation of Libya's legal obligation to surrender him to the ICC," it said.

Up to 8,000 Libyan soldiers are expected to train at two joint US-Bulgarian military bases in Bulgaria as part of post-war efforts to rebuild Libya, Defense Minister Angel Naydenov said Thursday.

Naydenov said he had approved Washington's proposal to train the troops but Bulgaria and the United States still had to work out the details.

A powerful blast caused serious damage to a foreign ministry building in the eastern Libyan city of Benghazi on Wednesday, witnesses said.

The explosion comes on the first anniversary of an attack by militants on the United States consulate in Benghazi, which killed four Americans, including the ambassador.

A blast killed a police colonel in Benghazi on Tuesday, a security services spokesman said, the latest in a string of attacks against police and soldiers in the eastern Libyan city.

Benghazi was the cradle of the 2011 revolt that toppled and killed dictator Moammar Gadhafi, but it has been hit by a wave of deadly attacks against security forces personnel.

The daughter of Libya's ex-spy chief Abdullah Senussi, who was reportedly kidnapped last week, has been freed, a member of her tribe said on Sunday.

Senussi was intelligence chief for Libya's long-time strongman Moammar Gadhafi, and his daughter Unud had completed a 10-month jail term when she was snatched on Monday.

The daughter of Libya's ex-spy chief Abdullah al-Senussi, who was reportedly abducted this week, was actually taken by special security forces for her own protection, a Facebook message said Thursday.

Senussi was the intelligence chief for Libya's long-time dictator Moammar Gadhafi, and his daughter Unud had completed a 10-month jail term when she was snatched on Monday.

Gunmen kidnapped the daughter of Libya's former spy chief Abdullah Senussi as she left a Tripoli jail after serving out a prison sentence, Justice Minister Salah al-Marghani said on Tuesday.

Senussi was the intelligence chief for Libya's long-time dictator Moamer Kadhafi, and his daughter Unud had completed a 10-month jail term when she was snatched on Monday.

Tunisia will set up buffer zones in the south of the country, along the borders with Libya and Algeria, to fight against "terrorism," Defense Minister Rachid Sabbagh said Thursday.

"Setting up these zones is necessary because of the current situation and to fight against the threats that hang over Tunisia," including "terrorism and arms trafficking," Sabbagh said.