Tunisian police have arrested four suspected Islamist militants accused of plotting to carry out attacks in the capital and to assassinate prominent politicians and journalists, an interior ministry spokesman said Wednesday.

The group, composed of three men and a girl, "was planning attacks against a commercial centre and a post of the National Guard (police) in Tunis", ministry spokesman Yasser Mesbah told AFP.

The police arrested the four in the capital's southern suburb of Ben Arous, Mesbah said, adding they had been communicating on Facebook.

Since the 2011 uprising that toppled longtime dictator Zine El Abidine Ben Ali, Tunisia has been battling an Islamist militant movement that has killed dozens of soldiers and police officers as well as civilians including 59 foreign tourists.

Security sources said on Monday they had found five arms caches in the south of the country near the border with war-ravaged Libya and seized large quantities of weapons.

Tunisia has been under a state of emergency for almost a year following a string of deadly attacks in 2015, claimed by groups affiliated with the Islamic State group and Al-Qaeda in the Islamic Maghreb.