Those released were part of a group of 41 foreign activists and seven Israelis detained in a Palestinian family's garden in the West Bank town of Mashah, through which the security barrier is set to pass.
Authorities had declared the area "a closed military zone".
The foreign activists were members of the International Solidarity Movement (ISM), and some came the United States, Britain, France, Italy, Germany and Sweden.
Israeli radio said the interior ministry had decided to expel one of the activists, an Italian woman, and warned the others not to disturb the work of the army.
The ISM has been leading an aggressive campaign in recent weeks to protest against the fence as well as roadblocks hampering freedom of movement in the West Bank.
In previous protests US activist Rachel Corrie was crushed to death by an Israeli army bulldozer in the Gaza Strip (news - web sites) town of Rafah in March and fellow ISM member Tom Hurndall from Britain was declared clinically dead after being shot in the same area a month later.
The arrests came as the United States warned that Israel's continued construction of a controversial West Bank security barrier may result in US financial sanctions, although a State Department spokesman stressed that no decision had yet been made.
Israel said last week it had completed the first 140 kilometer (85 mile) section of the barrier.
Israel says the barrier is essential to prevent Palestinian militants infiltrating from the West Bank to carry out anti-Israeli attacks.
