The Israeli army has raided the West Bank offices of the pro-Palestinian International Solidarity Movement (ISM) and arrested three people.
Soldiers confiscated computers and documents, and arrested an American, an Australian and a Palestinian.
Earlier in the day, Israeli forces arrested two British members of the group, who were trying to enter the Gaza Strip. They were taken for questioning at the border crossing between Israel and the Gaza Strip, according to ISM.
About 22 army jeeps surrounded the group's offices in the village of Beit Sahour.
Police said a 28-year-old woman from Chicago, an Australian woman, and a 22-year-old Palestinian were arrested. The military said it had arrested several people who violated the law in the village, but refused to release details.
The spokesman said the foreigners were in police custody, and were being questioned for entering a restricted military area. He added that the interrogation documents and other evidence - including the computers - will be used by the Interior Ministry to decide whether the foreigners should be deported.
The ISM is a pro-Palestinian organisation composed of volunteers who often act as human shields, placing themselves between Palestinians and the Israeli army.
In the past two months, an American member of the group, Rachel Corrie (23), was killed and two other foreign activists, an American and a Briton, were seriously wounded in separate incidents.
One of the wounded, Briton Tom Hurndall (21), is technically brain-dead and remains on life support in an Israeli hospital.