A British woman has been barred from leaving Egypt because she is on a list of foreigners under investigation over ties to foreign non-profit groups accused of fomenting unrest in the country.

An airport security official says she was ordered off a London-bound plane Friday in Cairo.

The official, speaking on condition of anonymity, says the woman works at a US non-profit group accused of illegally using foreign funds to finance activities to destabilise Egypt.

Sixteen Americans and 27 Europeans and Egyptians have so far been referred to trial on these charges. At least ten, including six Americans, have been barred from leaving the country.

The case has threatened Egypt-US relations and shocked "pro-democracy" groups.

There was no immediate comment from the British Embassy in Cairo.