RAMALLAH, West Bank, April 23 (Reuters) - Israel has taken measures against some 1,200 Palestinian prisoners on a hunger strike, denying them family visits and separating them from inmates not taking part in the protest, prison authorities said on Monday.

The open-ended strike, dubbed the "battle of empty stomachs" by organisers, began last Tuesday. The prisoners are demanding better jail conditions and for Israel to end detention without trial for Palestinians suspected of security offences.

"Privileges such as family visits have been revoked and items such as electronics have been confiscated," Sivan Weizman, a spokeswoman for the Israeli Prisons Authority, said.

Palestinian prisoners have long complained of the difficulty of securing family visits and the invasive searches visiting relatives have to go through.

The striking prisoners have said they would drink only water and salt until their demands are met.

Amani Sarahna of the Palestinian Prisoners Club, an advocacy group for Palestinians jailed by Israel, said prison authorities had conducted extensive searches in hunger strikers' cells, taking away salt from those refusing to eat.

"All the prisoners' belongings were confiscated except their towels and their shoes," Sarahna said.

The start of the strike last week coincided with the release of Khader Adnan, a prisoner who refused food for 66 days before agreeing to a deal under which he was freed. Adnan is a member of Islamic Jihad which has vowed to destroy Israel.

Organisers have called for rallies in the occupied West Bank and Gaza Strip in the coming days in support of the 4,800 Palestinians held in Israeli prisons. (Editing by Robin Pomeroy)