The bus was ripped open by the blast
Three people, including a 13-year-old boy, have died in an explosion at a petrol station in the Syrian capital Damascus, officials say.
Syrian Interior Minister Said Sammour said the tyre of a bus had exploded as it was being pumped.
The bus is believed to have been carrying Iranian pilgrims visiting the Sayyida Zeinab shrine for Shia Muslims.
Last year a car bomb killed 17 people on a road leading to the shrine. The bombing was blamed on Sunni militants.
But Mr Sammour ruled out an attack after Thursday's explosion.
He said the Iranian bus driver and two Syrian petrol station workers, including the boy, died when the tyre blew up as air was being pumped into it.
The BBC's correspondent in Damascus, Lina Sinjab, says there is a sense of confusion in the city behind the official statement.
This is because images of the blast and several witnesses have suggested that it may have been more than just a tyre explosion.
Initial reports had suggested that a bomb may have caused the blast.
Interior Minister Said Sammour ruled out a terror attack
In a country with tight security control, bomb explosions are very rare, our correspondent says.
Mr Sammour said there were no other casualties apart from the dead.
Our correspondent says witnesses saw parts of bodies scattered around but could not confirm to her whether the bus was full or empty when the blast occurred.
Witnesses and media reports had earlier said six people died.
Mr Sammour told state-run Syrian TV the bus was carrying Iranian tourists and passengers.
He said there were no pilgrims nearby when the blast happened.
The al-Sayyida Zeinab shrine, popular with Iranian pilgrims, is dedicated to the granddaughter of the Prophet Muhammad.