Mr Corbyn, the outgoing leader of the Labour Party, has been criticised in the past for receiving money from Press TV, which is funded by Tehran and is a division of the state broadcaster. Tensions between Iran and the US have been high following a strike at Baghdad International Airport, which killed Quds Force commander Qassem Soleimani. Speaking at the rally, Mr Corbyn said: “Today let’s recognise the horror that the families of those that died in the airliner travelling from Tehran to the Ukraine are suffering from now.
“Let’s be clear there can be no excuses here.”
“This is an appalling act and part of a whole pattern of appalling acts all across the region.”
He continued: “There’s no excuse for shooting down an airliner, there’s no excuse for a targeted assassination by one state against another.
“All this does is set off a spiral of violence and danger which will lead us to yet more wars in the future.”
The flight he was referring to was Ukrainian International Airlines Flight PS752, which crashed shortly after take off on Wednesday.
The plane was travelling to Kiev from Imam Khomeini Airport.
Initially, Tehran denied involvement.
But a statement from the military admitted the plane was shot down after being mistaken for a “hostile target”.
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Mr Johnson dismissed the claims as “absolute fiction”.
He continued: “The US has the right to protect its bases and personnel.
“Soleimani was responsible for many years for, amongst other things, arming the Houthis with missiles with which they attacked innocent civilians, arming Hezbollah with missiles – which again they used to attack innocent civilians.
“Sustaining the Assad regime in Syria, one of the most brutal and barbaric regimes in the world and of course supplying improvise devices to terrorists who I’m afraid killed and maimed British troops.”
He declared: “That man had the blood of British troops on his hands.”
Mr Corbyn said there was a a “real risk of going onto a full-scare war”.