The Palestinian Authority (PA), which has its headquarters in Ramallah, has regularly detained Hamas members, including MPs, over the past few years.
But the ongoing crackdown is a sign of the failure of a nearly year-old unity deal between Hamas, which controls the Gaza Strip, and the rival Fatah which dominates the PA.
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"We received information that 60 members of Hamas were arrested throughout the West Bank," a source from the Hamas headquarters in the territory, who asked to remain anonymous, told AFP without elaborating.
An official from the PA's security forces, also requesting anonymity, said there were around 40 arrests, but also gave no further details.
Under last April's unity deal, Hamas was to relinquish control of the Gaza Strip, paving the way for Palestinian general elections by the end of 2014.
But despite agreeing on a government of independents appointed in June, the deal stalled during a July-August war in Gaza between Hamas and Israel, and because of disputes over wages and control of the enclave.