The Israeli army said Thursday it had arrested between 20 and 30 Palestinian students in the occupied West Bank it accused of being "terror operatives" of Islamist group Hamas. 

Palestinian sources told AFP that dozens of students from Birzeit University were arrested as they were returning by bus from the village of Turmus Ayya where earlier this month Israeli troops demolished the family home of a Palestinian American awaiting trial on charges of shooting a Jewish student in the West Bank earlier this year. 

An Israeli army statement said: "Some of the apprehended terror operatives were directly involved in terror activities, including money transfers, incitement and the organisation of Hamas activities in Judea and Samaria," using the Biblical terms for the West Bank. 

Hamas, which runs the Gaza Strip and fought an 11-day conflict with Israel in May, is blacklisted as a terrorist organisation by the European Union and the United States. 

A late Wednesday statement announcing the arrests said "dozens of terror operatives" belonging to "a student cell" at Birzeit University had been detained in a joint operation involving the army, the police and the Shin Bet domestic security agency.  

An army spokesperson told AFP Thursday that the number held was between 20 and 30, and that the Shin Bet had taken over the investigation. 

Birzeit University in a statement voiced concern over the fate of its students and condemned the arrests as "a violation of all international laws and norms that guarantee students' right to movement".

"The university calls on the international community to intervene immediately to secure their release," the statement said.

Palestinian sources, who requested anonymity, said some of the students were expected to be released soon, but others faced protracted detention.