it's a shame more americans don't feel safe traveling to iran. it has some beautifully designed buildings.

We have seen a limited amount of video that is claimed to relate to the shootings. In one video filmed on the route to the aid site, purportedly on Sunday, people lie on the ground and an explosion is heard.

There is a "realistic possibility" this blast sound was a battle tank firing its main armament, says David Heathcote, an intelligence manager with security analysts McKenzie Intelligence, but he adds that "there could be other explanations". Another expert we spoke to said the source of the sound was unclear.

An audio recording provided to the BBC by international staff at the UK-Med field hospital about 3km away from the site captured two apparent explosions and protracted gunfire for over five minutes.