At least 11 people were killed on Tuesday after an explosion hit a bus carrying Tunisian presidential guards along a major street in the centre of the capital Tunis.
Security and presidential sources said the explosion was an attack, adding it was not immediately clear whether it was a bomb or an explosive device fired at the bus as it travelled along Mohamed V Avenue. Though some members of the presidential guard were among the dead, it wasn't immediately clear how many had been killed.
Bassem Trifi, a human rights lawyer, who saw the attack, told the AP it was "a catastrophic spectacle." He said the explosion hit the driver's side of the bus. "I saw at least five corpses on the ground," he said. "This was not an ordinary explosion."
Ambulances rushed from the scene and security forces quickly sealed off the area.
On Tuesday evening, Tunisia's prime minister and interior minister visited the scene, but neither was able to say who was responsible for the attack.
Although terrorists attacks are on the rise in Tunisia, previous operations have targeted tourists, and not government entities. This year alone, Tunisia has suffered two major attacks on its tourism industry. A gunman killed 38 foreigners at a beach hotel in June and in March, gunmen killed 21 tourists at the Bardo Museum in Tunis.
Islamic State claimed both previous attacks, but there has been no claim of responsibility for today's.
And IS is not the only possible culprit. The army has also been fighting a low-level insurgency waged by other Islamist militant group in the mountains near the Algerian border. In recent months, the militants have hit checkpoints and patrols in rural areas.
Ten days ago, security forces increased their presence in Tunis, as a reaction to the attacks in Paris, and earlier in the month police claimed to have broken up a terror cell that was planning attacks against tourists. Just Monday, government sources told AFP that Tunisia's ex-president Moncef Marzouki was the target of an assassination plot.
After Tuesday's attack, many circulated the hashtag #PrayForTunisia on Twitter, an illusion to the memes that spread after the Islamic State attacked Paris earlier this month.