Seven Israeli human rights groups demanded an inquiry on Wednesday into the "inhuman" treatment meted out to Palestinians taken prisoner during Israel's offensive on the Gaza Strip.

Evidence collected from detainees provided a "shocking portrayal of the harsh, inhuman and degrading conditions in which Palestinian prisoners were held during the initial days of their incarceration," they said in a statement.

"Many detainees - minors as well as adults - were held for many hours, sometimes for days, in pits dug in the ground, exposed to bitter cold and harsh weather, handcuffed and blindfolded.

"These pits lacked basic sanitary facilities...detainees went hungry.

"Some of the detainees were held near tanks and in combat areas, in gross violation of international humanitarian law."

The groups submitted a complaint to Israel's attorney general and the military judge advocate general, urging an independent and comprehensive investigation.

The statement also spoke of "incidents involving extreme violence and humiliation by soldiers and interrogators" and added that separate complaints would follow about that.

"Israel's indifference to its moral and legal obligations to detainees is particularly objectionable in view of the fact that official spokesmen have repeatedly declared that the Israeli Defense Forces prepared at length for the Gaza operation," said Bana Shoughry-Badarne, director of the legal department of the Public Committee Against Torture in Israel.

"It seems that, during these lengthy preparations, the basic rights of the detainees and captives were completely forgotten, rights that must be protected regardless of the detainees' legal status and whether or not their incarceration is justified."

The statement didn't give any figures for the numbers of arrests, but the army reported making dozens of members of the Islamist Hamas movement prisoner during the 22-day assault that ended Jan. 18 with more than 1,300 Palestinians dead, local doctors said.

The other groups involved were the Association for Civil Rights in Israel, Hamoked: Center for the Defense of the Individual, Physicians for Human Rights, B'Tselem, Yesh Din and Adalah.