The United States embassy in Tunisia has warned its citizens to avoid a major shopping mall in the capital Tunis on Sunday because of a reported threat of a potential militant attack there.

Tunisia is under a state of emergency following a suicide bomb attack on a presidential guard bus in Tunis last month. That followed two major militant gun attacks on a Tunis museum and a beach hotel targeting foreign tourists.

A statement late on Saturday advised US citizens to stay away from the Tunisia Mall in Berges du Lac area in the capital on Sunday because a "report of unknown credibility indicates the possibility of a terrorist attack."

It gave no further details. But Tunisia security forces have been on high alert since the November 24 suicide bombing that killed 12 presidential guards as they boarded a bus to start their tour of duty.

The November attack on a main boulevard in the capital underscored the vulnerability of Tunisia to Islamist militancy, following assaults on the Sousse seaside tourist hotel in June and the Bardo Museum in Tunis in March, all claimed by Islamic State.

One of the Arab world's most secular nations, Tunisia has become a target for militants after being praised as a symbol of democratic change in the region since its 2011 uprising ousted autocrat Zine Abidine Ben Ali. - Reuters