The bomb exploded on a bus carrying Tunisian presidential guards. The president of Tunisia, Beji Caid Essebsi, was not on the bus at the time. He has declared a 30-day state of emergency.
The perpetrators remain unidentified, according to government spokesman Walid Lougini.
Yesterday's attack is the third major terrorist incident in the country this year. In March, Islamic State militants assaulted the Bardo Museum in Tunis, killing 20 people.
And in June, IS jihadis killed 38 people in the beach resort of Sousse.
Mike Farho, the pastor of Sousse Christian Church, thanked the UK and Premier for its support as the country comes under attack from terrorists.
He told us: "People really love their country and they're very concerned for it. They don't understand how this could be happening now. They really want to see their country move forward in freedom and democracy, so they appreciate the people of Great Britain and England supporting them in so many different ways.
"Since the terrorist attacks [in Sousse] we've gone from 47 hotels open to 19 hotels open. It's very rare now to have a tourist come to church because the ones that are here stay in their hotels.
"We need Christ as our Saviour and Christ as our force in this world, and not the political arguments that are going around."
Listen to Premier's Aaron James speaking to Mike Farho:
