TRIPOLI (Reuters) - The trial of Muammar Gaddafi's son Saif al-Islam may be delayed to include any relevant testimony obtained via interrogation from the country's former spy chief who was arrested on Wednesday, a government official said on Thursday.

Muammar Gaddafi's former spy chief Abdullah al-Senussi (C) is seen in custody in Tripoli in this undated handout picture. REUTERS/Libyan National Guard/Handout

Government officials said in August that Saif al-Islam's trial on war crimes charges - the most high-profile prosecution of a figure from his late father's entourage to date - was due to begin in September.

But the arrest on Wednesday of Abdullah Senussi, the former spy chief known as "Gaddafi's black box", appears to have pushed that date back, postponing a trial that a lawyer from the International Criminal Court (ICC) has already said is unlikely to be fair.

Senussi was handed over to Libya by Mauritanian authorities on Wednesday after being captured in the West African state in March, triggering a tug of war between Libya, France and the ICC for his extradition.

"We expect the trial of Saif al-Islam to be delayed a little because Abdullah Senussi will be able to provide new information that can be used in Saif's trial," Taha Ba'ara, a spokesman for the prosecutor general's office, told Reuters on Thursday.

Libya's new rulers, who aim to draw up a democratic constitution, are keen to try Gaddafi's family members and loyalists at home to show the country's citizens that those who helped Gaddafi stay in power for 42 years are being punished.

HUMAN RIGHTS CONCERNS

Saif al-Islam will have to respond to charges which include financial corruption, murder and rape, according to a statement from Justice Minister Ali Ashour in April.

The charges, which he denies, relate to crimes he allegedly committed during the NATO-backed revolt that toppled his father last year prompting a fearful Senussi to flee.

Ba'ara said a government delegation including the Libyan army's chief-of-staff, the finance minister, and a member of the prosecutor general's office had travelled to Nouakchott, the capital of Mauritania, to escort Senussi back home.

Recognisable from his trademark tightly curled hair, a heavily bearded Senussi was shown in a local press photograph getting out of a helicopter in Libya.

Ba'ara said that Senussi's interrogation had begun on his arrival at a Tripoli prison after he had undergone medical tests.

"We will guarantee all his rights. If he asks for a lawyer then we don't mind providing him with one during interrogation, but if he doesn't ask for one then we cannot force him to take one," Ba'ara said.

Human rights activists worry that a weak central government and a relative lack of rule of law mean that legal proceedings - both for Senussi and for Saif al-Islam - will not meet international standards.

On Wednesday, rights groups called on Libya's government to hand over Senussi to the ICC where an arrest warrant for him remains in force.

In July, a war crimes lawyer who was detained in Libya for three weeks on spying allegations said her experience had shown it was impossible for Saif al-Islam to get a fair trial in his home country.

(Writing By Hadeel Al-Shalchi; Editing by Andrew Osborn)

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