"There is a very high terrorist alert in the city of N'Djamena, which has forced us to ban all public demonstrations," RFI website quoted Communication Minister Abdreman Koulamallah as saying.

It added that the alert followed reports that "three terrorists, probably from Boko Haram, managed to infiltrate N'Djamena over the weekend".

It cited official sources who said that the suspected militants were still at large.

Rumours of an imminent attack were sparked by heavy deployment of security forces on major roads in N’Djamena.

At least 38 people were killed and dozens more injured in a Boko Haram attack in N'Djamena in 2015.