William Hague last night warned Britons to leave the Congolese city of Goma after Rwandan-backed rebel fighters arrived on its outskirts.
The Foreign Secretary said the "rapidly deteriorating security and humanitarian situation" in eastern Democratic Republic of the Congo (DRC) meant it was too dangerous to remain in Goma.
More than 150 rebels and two soldiers have been killed since intense fighting broke out on Thursday between the 23 March Movement (M23) and the Congolese army.
An M23 spokesman was reported to have said his forces were ready to take the provincial capital, which is a centre for aid operations in the region. Only a handful of Britons are believed to remain in Goma but Mr Hague said they should now leave.
"I strongly condemn the M23's advance towards Goma and call on it immediately to desist from further violence," he said in a statement.