This is from the Telegraph.
As the article notes at the end the U.S. has increased the funding of covert operations inside Iran to the tune of 200 million. It is just possible that the U.S. is behind the explosion. On the other hand it may simply be an accident.
Iranian military convoy rocked by mystery explosion
Iran's Revolutionary Guards have launched an urgent inquiry after a mysterious explosion wrecked a military convoy in Tehran, killing at least fifteen people and injuring scores more.
By Con Coughlin Last Updated: 1:55PM BST 25 Jul 2008
The explosion took place in the Tehran suburb of Khavarshahar as the military convoy left a munitions' warehouse controlled by the Revolutionary Guards. According to reports received by Western officials, the convoy was taking a consignment of military equipment to Hizbollah, the Shia Muslim militia Iran supports in southern Lebanon, when the explosion occurred.
Senior Revolutionary Guard commanders immediately imposed a news black-out following the explosion, even though it could be heard throughout the capital Tehran, and no details of the incident have so far appeared in the Iranian media.
But Western officials yesterday said they had received reports that the explosion took place in Tehran on July 19, and that the Revolutionary Guards had launched an investigation into the causes of the blast.
"This was a massive explosion that was heard throughout Tehran," one official told the Daily Telegraph. "Even though lots of people were killed the Revolutionary Guards are trying to conceal what really happened."
Iran is believed to have recently stepped up arms shipments to Hizbollah in preparation for any future armed confrontation with the West over its controversial nuclear enrichment programme.
The Revolutionary Guards' investigation into last weekend's explosion is understood to be looking into the possibility that it was caused by sabotage. Iran has suffered a number of unexplained explosions in recent months, including an explosion at a mosque in Shiraz, which had been holding a military exhibition, and another incident at a missile site that killed dozens of Iranian technicians.
Last month Seymour Hersh, the respected American investigative journalist, reported that US President George W Bush had authorised up to $400 million (£200 million) to fund a major escalation of covert operations against Iran to destabilise the regime.