A Hamas statement said 120 party members had been arrested or summoned to report to security services since Wednesday.
It said detainees are from Aida refugee camp in Bethlehem, Askar refugee camp in Nablus, Jerusalem-area village Qatanna and Qalqiliya.
On Wednesday, Hamas and Palestinian rights group said around 60 people were detained overnight.
The Palestinian Center for Human Rights condemned the campaign and called on the Palestinian government in Ramallah to fully comply with the law and stop political arrests.
Palestinian Authority security services spokesman Adnan Dmeiri said Thursday the arrests were conducted legally and not based on the detainees’ political views. He said Hamas was exaggerating the number of arrests, but did not provide alternative figures.
Hamas seized control of Gaza in a brief civil war in 2007, ushering in a half decade of rivalry with Fatah-dominated authorities in the West Bank. Both sides accuse regularly each other of politically-motivated arrests.