Iran has summoned the UK ambassador as hardline militia members mass outside the British embassy in Tehran.

The British ambassador to Iran earlier denied taking part in anti-government demonstrations after he was held by Iranian authorities during protests over a fatal plane crash.

Iranian authorities detained Rob Macaire on Saturday on suspicion of organising, provoking and directing radical actions, but an Iranian news agency later said he had been summoned over his attendance at an "anti-government rally".

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