Israeli forces in the West Bank have arrested at least 20 members of the Palestinian militant group Hamas.
Those arrested, in overnight raids all over the West Bank, included three members of the Palestinian parliament.
Israel regards Hamas as a terrorist organisation, but has not said why the arrests were carried out.
Palestinian human rights groups condemned the arrests, saying they aimed to undermine the reconciliation talks between Palestinian factions.
Israel holds more than 4,500 Palestinians in its jails, 12 of them members of the Palestinian parliament, according to Palestinian reports.
Israel has occupied the West Bank since 1967, settling more than 450,000 people in the territory.
In the 2006 Palestinian parliamentary elections Hamas won 74 seats to rival Fatah's 45 seats in 132 seat parliament.
Armed clashes erupted in Gaza between the two faction sides. Hamas violently forced out Fatah from Gaza in June 2007.
Hamas continues to control Gaza while Fatah remains dominant in the West Bank. In May 2011 Fatah and Hamas signed a reconciliation deal but it has not yet been implemented.