Boris Johnson's calls for protests outside the Russian embassy risk retaliation in Moscow, a former spy chief has warned.
Sir John Sawers said the consequences for the security of Britain's embassy in Russia should be considered when urging demonstrations and highlighted the attack on the UK's base in Iran by protesters in 2011.
The ex-MI6 chief said it had been a mistake not to take military action at the start of the Syrian civil war and Britain had "vacated the theatre".
During an emergency Commons debate on Syria, the Foreign Secretary called for demonstrations outside the Russian embassy in protest at the bombing of Aleppo.
Sir John told BBC Radio 4's Today programme: "We all have to be a little bit careful and mindful of the security of our embassy in Moscow when we think about calling for demonstrations here in London.
"We all recall what happened to our embassy in Tehran three or four years ago. I don't think that would happen in Moscow but we need to be careful about the consequences of things that we call for."
Sir John said the worsening crisis was a direct consequence of Britain's decision "not to engage ourselves".
"We vacated the theatre and the Russians have moved in," he said. "It certainly was a mistake. Chemical weapons were being used against civilians in Damascus by their own regime."
Sir John said the balance of power globally had changed and Russia and China were now much more powerful than they were in the past.
"In some ways we are moving into an era which is as dangerous, if not more so, than it was in the Cold War because we don't have that level of focus on the strategic relationship between Washington and Moscow," he added.
It comes as peace campaigners claimed p rotesting outside the Russian embassy over Syria would increase the "hysteria and jingoism" that is being "whipped up" against the federation.
The Stop the War Coalition claimed the Government was fuelling anti-Russian sentiment in an attempt to "justify" an escalation of British military intervention.
Mr Johnson called directly on the campaign group on Tuesday to stage embassy protests over the continued attacks by Russian warplanes on the stricken city of Aleppo.
But Stop the War vice chairman Chris Nineham said the organisation would not get involved.
"The reason for that is our focus is on what our Government is doing," he told Today.
"There's a very good reason for this, because we can make a difference to what Britain does, we can make a difference to what our allies do to a certain extent and we have done.
"But, if we have a protest outside the Russian embassy it wouldn't make a blind bit of difference as to what (President Vladimir) Putin does because we are in Britain and we are in the West.
"And, not only that - a protest outside the Russian embassy would actually contribute to increasing the hysteria and the jingoism that is being whipped up at the moment against Russia."
He added: "What we are saying is there is a hysteria which is being organised by politicians and the media against Russia to see Russia as the only problem in Syria."
Mr Nineham said the Foreign Secretary's calls for demonstrations were "characteristically trivialising".
Mr Johnson told MPs Russian President Vladimir Putin was in danger of turning his country into an ''international pariah'' with his continued support for the regime of President Bashar Assad.
''It is the UK week after week that is taking the lead together with our allies in America and in France, all the like-minded nations, in highlighting what is happening in Syria to a world where, I'm afraid, the wells of outrage are growing exhausted,'' he said.
''There is no commensurate horror, it seems to me, amongst some of those anti-war protest groups. I'd certainly like to see demonstrations outside the Russian embassy. Where is the Stop the War Coalition at the moment? Where are they?''
Mr Johnson has previously angered Russia by claiming that its forces may have been guilty of war crimes last month when air strikes hit a UN aid convoy near Aleppo, finally ending a fragile ceasefire.