The Interior Ministry confirmed Friday the expulsion of eight Belgians who were planning to attend a conference in the West Bank town of Ramallah.
Four other foreigners, among them three Brazilians, were in custody Friday at Ben-Gurion airport awaiting deportation.
A government spokesperson said that the interior ministry had information that the foreigners, among them six women, were likely to disturb the peace.
The Belgians were among a 12-member group planning to take part in a four-day "World Social Forum" in Ramallah, Palestinian sources said.
They were detained by immigration officials when they arrived in Israel on Thursday. The group flew back to Europe aboard a German Lufthansa airliner Friday morning, Belgian foreign ministry spokesman Didier Seeuws said.
Belgium was not informed of the reasons for the expulsions and has protested the decision to Israel. Among those expelled was Pierre Galand, chairman of a Belgian-Palestinian association.