A massive explosion at a military arms depot near the Iranian capital Tehran on Saturday killed 17 Revolutionary Guards and wounded 15, a spokesman for the elite fighting force told the semi-official Fars news agency.
Officials said the blast was an accident which happened as troops were moving munitions at a base in Bidganeh, near the town of Shahriar, some 45 km (28 miles) west of Tehran.
The explosion shook homes and rattled windows for miles around, at a time of mounting tension with Israel over Iran's nuclear programme.
Today at 13:30, (9:00 a.m. British time), an explosion happened in one of the Revolutionary Guards' bases while a consignment of explosive devices was being moved out from the arsenal, besides that some munitions in the arsenal exploded which created a terrifying sound, Revolutionary Guards spokesman Ramezan Sharif told state
Sharif initially said 27 people had been killed but later revised that figure down to 17.
Residents in western suburbs of Tehran told Reuters they had felt the blast, some assuming it to be a moderate earthquake.
The explosion started a fire at the base which raged for hours. Surrounding streets were closed and reporters were kept away from the scene.
Some media reported there had been two explosions and the head of Iran's Red Crescent organisation said there was a risk of further blasts.
Mahmoud Mozafar told the Mehr news agency that only six paramedics had been allowed into the Amir Al-Momenin military base and that thick smoke was hampering the rescue operation.
There were no reports linking the blast to any air strike or other attack. Tension has risen in recent weeks between Iran and its enemies Israel and the United States, which have not ruled out attacking facilities whose occupants they believe are working towards making nuclear weapons.
Sharif denied what he said was speculation in the Western media that the military base was linked to Iran's nuclear programme.
This blast is not related to any nuclear tests that some foreign media have reported, he told Mehr.
Tehran denies Western accusations, that were given some credence by a report from the UN nuclear agency this week, that its nuclear programme has military ends.
On October 12 last year a similar blast at a Revolutionary Guards munitions store killed and wounded several servicemen in Khoramabad, western Iran. Authorities said that explosion was an accident too.
(Additional reporting by Mitra Amiri and Hossein Jaseb; Writing by Robin Pomeroy; Editing by Tim Pearce)