A large explosion aboard a bus targeting security forces in the Tunisian capital of Tunis has killed 14 on the city's central Mohammed V Avenue with many more injured, according to the Tunisian Ministry of Interior.

The Tunisian government has denounced the attacks as a terrorist act but at present there are no clear indications of what caused the blast . Tunisian state media reported the explosion targeted a military bus carrying members of the presidential guard.

People staying at the Hotel du Lac reported witnessing the explosion which took place at an intersection in an area dominated government buildings at around 5pm. The blast took place between the Tunisian Ministry of Toursim and the offices of the now defunct Rassemblement Constitutionnel Démocratique, the ruling party of former leader Ben Ali who was overthrown in 2011. The scene of the explosion is also just a short distance from the offices of the Ministry of the Interior.

Video footage apparently from the immediate aftermath of the bombing has shown a large number of police and ambulance vehicles dispatched to the scene. A cordon is now reportedly in effect to keep onlookers away.

Tunisia has been plagued by security problems over the past year. Islamic State (Isis) militants killed 21 people in Tunis, most of them European tourists, in an attack against the Bardo Museum, in March.

The country witnessed its worst ever terror attack in June when a lone gunman, also a supporter of IS, killed 38 in the Mediterranean resort of Sousse. Most of the victims were Britons.

Tunisian authorities had been wary of a possible car bomb attack in central Tunis. According to state news, security forces banned cars from travelling in some in areas of the city in September, following warnings of a possible attack,

A source within the interior ministry told the state news agency TAP that car bombs or an attack by suicide bombers wearing bomb belts could target certain parts of the capital.