A blast ripped through a bus carrying Iranian pilgrims in Damascus on Thursday, killing at least three people in an incident Syria said was an accident and not a terrorist attack.

'There was no terrorism factor behind the bus incident,' Syrian Interior Minister Said Sammour said. 'The bus entered a petrol station to have one of its burst tyres inflated and the tyre exploded. Three people were killed.'

Witnesses said earlier a bomb had hit the bus near the Shi'ite shrine of Sayyeda Zainab, killing six people and destroying the rear of the bus and causing damage to nearby buildings.

'Body parts are still scattered around the bus,' one of the witnesses told Reuters from the Sayyeda Zainab area in Damascus.

The blast took place as Saeed Jalili, Iran's chief nuclear negotiator, was visiting Damascus for meetings with Syrian officials.

Syrian security forces deployed in the area, a popular destination for Shi'ites from Iran and Lebanon, and were investigating the blast. – Reuters