Families of British embassy staff are being evacuated from Iran amid escalating clashes between security forces and demonstrators protesting over this month’s disputed presidential election.
The Foreign Office also tightened its advice on travel to the country, warning British nationals against all but essential visits.
Riot police used tear gas and fired live bullets in the air to disperse a rally in central Tehran on Monday in an apparent sign that the regime of president Mahmoud Ahmadinejad is taking a tougher line with protests.
Near-daily rallies on the streets of the Iranian capital have drawn crowds numbering hundreds of thousands over the past week.
But the elite Revolutionary Guard ordered demonstrators to end “sabotage and rioting activities” and be prepared for a “revolutionary confrontation” with security forces if they continue their protests.
In a statement, the Foreign Office said: “The ongoing violence has had a significant impact on the families of our staff who have been unable to carry on their lives as normal. As a result, we are withdrawing dependants of embassy staff until the situation improves.
“We do not believe that it is necessary to reduce the number of staff at this time, however we are monitoring the situation with the utmost vigilance. The security of our staff is of paramount importance.”
The statement said it was hoped that families could return “as soon as possible”.
British citizens already in Iran have not been advised to leave the country, but are being warned to avoid demonstrations and large public gatherings.
The Foreign Office said diplomats were monitoring the situation with “the utmost vigilance”