A senior member of Tunisian hardline Salafist group Ansar al-Sharia has been arrested in connection with the attack on the US embassy in Tunis earlier this month, the interior ministry said on Monday.

"Hassen Brik, who is the subject of a police inquiry, was arrested on Sunday in the connection with the investigation," ministry spokesman Khaled Tarrouche told AFP.

Supporters of the extremist group's leader Seif Allah Ibn Hussein, who is also wanted by the police, said on their Facebook page that the preacher "Hassen Brik was arrested in the El-Khadra district of Tunis on the pretext of checking his identity."

His arrest adds to the 96 protesters held following the attack on the American embassy in Tunis on September 14, which left four people dead and dozens wounded.

Since then, the police have been searching for Salafist leaders, including Ibn Hussein who is also known as Abu Iyadh and who has managed to escape arrest several times since the deadly violence in which he has been implicated.

The ruling Islamist party Ennahda has been strongly criticised for failing to clamp down on Tunisia's Muslim extremists, who have carried out numerous acts of violence since last year's revolution that ousted former strongman Zine El Abidine Ben Ali.

The party's veteran leader Rached Ghannouchi vowed, in an interview with AFP on Friday, that Ibn Hussein would be hunted down and arrested.