Egyptian authorities stopped an American woman from boarding a flight to Germany on Thursday since she currently faces trial over illegal funding of civil society groups, an airport official said.
Mary Elizabeth Whitehead, 56, is one of dozens of people who have been barred from leaving Egypt during a judicial investigation into the funding of "pro-democracy" organisations, said the official, who asked not to be named.
Whitehead, who had taken no luggage with her, tried to board the plane minutes before it was due to take off but was ordered to turn back by airport security, he said.
Groups caught up in the probe, including the US-funded National Democratic Institute and International Republican Institute, are banned from working in Egypt. Some of the Americans under suspicion have taken refuge in the US embassy in Cairo.
The case has caused a crisis in relations between Egypt and Washington, with Congress warning it may cut the $1.5 billion in annual aid to Egypt if the crackdown drags on.
Government officials accuse the organisations of interfering in Egypt's internal affairs and carrying out political activities unrelated to their "civil society" work.
Egyptian civil rights campaigners say the investigations come as retaliation by Egypt's ruling military council against "pro-democracy" groups that have been among the army's harshest critics since it took power following last year's ouster of longstanding president Hosni Mubarak.
The government and the ruling military council say the case was initiated by the judiciary and is out of their hands.
The 43 accused, including about 20 US citizens, are due to go on trial on Sunday, charged with working in the country without proper legal registration, according to a judicial source.