British Foreign Secretary William Hague has withdrawn all diplomatic staff from its Embassy in Syria and suspended its services.
Hague said the embassy in Damascus had been retained "despite the violence" for communication purposes and to monitor events.
The UN's rights council has passed a resolution condemning "systematic violations" against civilians.
Meanwhile, Syrian forces have tightened their grip on Homs, a day after they launched a ground assault on the Baba Amr district.
Communication with the area has been largely cut off, and people are struggling to get in or out.