Israeli forces have detained the Speaker of the Palestinian parliament at his home in the West Bank.
Israeli forces had twice before surrounded Mr Dweik's home
Aziz Dweik, also a key member of Hamas, which controls the government, was held after 20 Israeli vehicles surrounded his home in Ramallah.
The Israeli military confirmed the detention, saying Mr Dweik was a legitimate target as a Hamas leader.
Palestinian Prime Minister Ismail Haniya condemned the action, accusing Israel of "piracy".
He said: "We urge all Arab and international parliamentarians to condemn and denounce this crime and to secure the release of Aziz Dweik and all jailed ministers and lawmakers."
Israel detained eight members of the Hamas-led government and 20 MPs on 29 June. Palestinians called that an act of war.
The detentions followed the capture of an Israeli soldier by Palestinian militants in June.
An Israeli army spokesman, confirming Mr Dweik's detention to Reuters news agency, said: "Since Hamas is a terrorist organisation, he is a target for arrest."
Israel has launched a number of strikes in Gaza in recent days
Israeli forces had twice previously surrounded Mr Dweik's home but had not arrested him.
Mr Dweik's wife told Reuters on Saturday: "We were sitting home peacefully, normally. Then we heard knocking on the door.
"He went down because the army was there. He opened the door. They saw him in his pyjamas and asked him to go with them."
Red Cross request
The move came as Israel continued operations in the Gaza Strip.
Late on Saturday a Palestinian boy was killed in an air strike in the southern town of Rafah, local medical sources said.
Earlier, at least four people - two militants and two civilian teenagers - died in separate Israeli attacks in the area.
Israeli soldiers and tanks moved back into the southern Gaza Strip three days ago, conducting searches for the detained soldier, Cpl Gilad Shalit.
Also on Saturday, Hamas issued a statement rejecting a Red Cross request for a visit to Cpl Shalit, saying it was "not appropriate at a time when more than 10,000 Palestinian families are denied to visit their prisoners".
Israeli Cabinet minister Ophir Pines said: "We allow people to see Palestinian prisoners... people know where they are and we allow access by international organisations".