"They lie that the United States is our enemy - our enemy is here," cries dozens of protesters outside a university in Tehran, in videos on Twitter that Reuters noted.

Iranian authorities have commanded security forces in the city on Sunday as they await continued protests.

At the same time, members of the Basij paramilitary militia, which is subordinate to the Iranian Revolutionary Guard, have gathered outside the UK embassy in the city and demand that it be closed.

Britain's ambassador has been called for questioning after taking part in demonstrations against the Iranian leadership, Reuters writes. He was arrested on Saturday, but quickly released again.