Saif al-Islam Gaddafi is seen sitting in a plane in Zintan in this file image from 19 November 2011.

Geneva - The International Committee of the Red Cross (ICRC) said on Thursday it had made its second visit to Saif al-Islam Gaddafi, the son of Libya's former leader, detained by militia fighters in the west of the country.

“We visited him yesterday ... It was a short visit by ICRC delegates including a doctor,” ICRC spokesman Steven Anderson told Reuters.

“It was in keeping with our standard procedures. We cannot comment on his condition. He wrote a Red Cross message to a member of his family,” he added.

The visit came six months after Libyan militia fighters captured Saif al-Islam as he took refuge in the Sahara desert, following the overthrow and killing of his father Muammar Gaddafi in Libya's uprising.

Saif al-Islam's capture and continued detention by militia fighters has raised concerns about how he is being held and his chances of a fair trial in Libya.

Libya's new justice minister has said he wants to try Saif al-Islam for murder, torture and other offences allegedly committed during the crackdown on the revolt. If convicted, he could face the death penalty.

The International Criminal Court (ICC) has also issued an arrest warrant for Saif al-Islam to face charges of crimes against humanity.

Last month a senior defence lawyer at the ICC said Saif al-Islam had been physically attacked and had been denied medical treatment, despite suffering from toothache. Libyan authorities dismissed the report.

Saif al-Islam was still detained in the western city of Zintan, Anderson said, declining to say whether he was still under house arrest.

The ICRC only shares its findings on prisoners' conditions and treatment with the detaining authorities, a code of practice that enables it to gain a unique level of access but means that most of what it discovers is kept secret.

The ICRC first visited him in Zintan on Nov 22 shortly after his capture.

Libya said earlier this month that it would complete its investigation into Saif al-Islam within weeks and asked the International Criminal Court to once again hold off ordering his transfer. - Reuters