The Palestinian parliamentary speaker detained by Israel on Sunday has been taken to hospital with chest pains and dizziness, the Israeli army says.
Dweik was held after 20 Israeli vehicles surrounded his home
A spokesman for Aziz Dweik said he was taken to hospital after being beaten by Israeli guards. The army, which is holding him, denied the claims.
Mr Dweik, who is a key member of the governing Hamas movement, was detained in a raid on his home in the West Bank.
The Israeli military said Mr Dweik was a legitimate target as a Hamas leader.
Israel has detained about 30 MPs and a third of the Palestinian cabinet in the past six weeks, following the capture of an Israeli soldier by Palestinian militants in June.
Palestinian officials have called on the international community to intervene to secure their release.
A Hamas spokesman in Gaza said that Mr Dweik was taken to hospital "after being severely beaten".
The Israeli army said a prison doctor had examined Mr Dweik after he had complained of dizziness and chest pains, and decided to transfer him for further tests to a hospital in Jerusalem.
"He underwent tests at the hospital and will remain under observation," a spokesman told the Agence France Presse news agency.