The United States has urged its citizens to avoid a shopping centre near the Tunisian capital because of the threat of an attack on Sunday.

"We wish to advise you that a report of unknown credibility indicates the possibility of a terrorist attack at the Tunisia Mall in Berges du Lac on Sunday, December 20, 2015. We advise you to avoid the area," the US embassy in Tunis said.

There was no immediate comment from the Tunisian authorities.

Tunisia is grappling with a growing extremist threat that has seen several major attacks claimed by ISIS  this year targeting tourists and security forces.

Twenty-one foreigners and a policeman were killed at the Bardo National Museum in Tunis in March and 38 people, mainly British holidaymakers, were gunned down at the seaside resort of Sousse in June.