The Sudanese Media Centre quoted an unnamed security source as saying Turabi and his aides were supporting Darfur's insurgent Justice and Equality Movement (JEM) financially and logistically.

"The source has not ruled out presenting Turabi for trial," it said. It did not name specific charges.

Government sources outside state security, including the Ministry of Justice, have so far not commented on the reasons for Turabi's detention.

Turabi's supporters on Monday denied any link to JEM.

Members of his opposition Popular Congress Party said he was arrested to silence him in the build-up to a ruling from the International Criminal Court on whether to issue an arrest warrant against President Omar Hassan al-Bashir for alleged war crimes in Darfur.

The United States Embassy in Khartoum on Monday said it was "concerned" about the arrest of Turabi and another senior official from his party, adding Sudan needed to respect freedom of expression in the build-up to elections planned in 2009.

Turabi was al-Bashir's ideologue until they split in a power struggle in 1999/2000.