Palestinians seized during Israel's operation in Gaza faced "appalling" conditions and "inhuman" treatment, Israeli human rights groups have said.

The seven groups say they have gathered 20 testimonies which indicate detainees were kept in pits without shelter, toilets or adequate food and water.

Some detainees also said they had been held near tanks and in combat areas, the groups said.

The Israeli military says it is investigating the allegations.

The accounts were gathered by the Public Committee Against Torture in Israel (PCATI) and Hamoked, the Center for the Defense of the Individual, from Palestinians now being held in Israel.

'Gross violation'

"The reports indicate that... 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," the groups said in a statement.

"These pits lacked basic sanitary facilities... while food and shelter, when provided, were limited, and the detainees went hungry," it said.

The groups accused the military of "gross violation of international humanitarian law" by holding some of the detainees close to tanks.

Incidents involving "extreme violence and humiliation by soldiers and interrogators" were also reported, the statement said, without giving details.

"We were handcuffed and blindfolded. They put us in a three-meter deep ditch with some 70 other people," Majdi Muhammad Ayid al-Atar, 43, from northern Gaza described, in one of the testimonies.

"We spent two days there without any food, water or blankets. They also didn't let us go to the toilet. Afterwards they moved us to another ditch. The soldiers kept beating anyone who dared ask for anything," he was quoted as saying.

Lengthy preparation

The groups have addressed a written complaint to the Military Judge Advocate General, and Israel's Attorney General, Meni Mazuz.

Attorney Bana Shoughry-Badarne, Legal Director of PCATI, said the findings were "particularly objectionable" as the Israeli military had repeatedly stressed that it "prepared at length for the Gaza operation".

"It seems that, during these lengthy preparations, the basic rights of the detainees and captives were completely forgotten," she said.

She said the groups had the names of 29 people who had been detained, 25 of whom were still being held.

The other groups were the Association for Civil Rights in Israel, Physicians for Human Rights, B'Tselem, Yesh Din and Adalah.