Blows to the head and sleeping in insect-infested beds are among numerous examples of "degrading" and "inhuman" treatment of Palestinian detainees by Israeli interrogators, according to a new report from Israeli human rights groups.

The 54-page report from HaMoked and B'Tselem, released on Wednesday, alleges that the treatment of detainees is at times "tantamount to torture". It documents physical abuse by Israeli interrogators both in the field and at the Shikma detention facility in the southern Israeli city of Ashkelon.

"[One Palestinian] was beaten until he passed out. Another detainee related that police officers photographed themselves next to him as he lay handcuffed on the ground after being beaten for about half an hour," the report stated, noting that abusive conditions had been "used systematically against Palestinians interrogated at Shikma".

The findings are based on the testimonies of 116 Palestinians interviewed between August 2013 and March 2014, along with dozens of affidavits and medical records.

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Israel's high court prohibited the use of torture in 1999 and explicitly outlawed some of the specific interrogation tactics detailed in the report. At the time, the court said that interrogators would not be immune from prosecution over prisoner abuse.

The cell was full of cockroaches [and] very dirty. The blankets stank. After about 10 days, I had a rash all over my body. Ibrahim Sabah, 19

"One of the things we noticed is that certainly there was a clear decline in cases of torture and ill-treatment, which was very common before the ruling," B'Tselem spokesperson Sarit Michaeli told Al Jazeera. The issue of detainee treatment has come under the spotlight again in recent months, amid a wave of violence and arrests since October.

"[While] there is a renewed escalation in the amount of violence in the West Bank, that does not justify increasing and using these kinds of methods," Michaeli said.

Researchers found that interrogations by the Israel Security Agency are a lengthy component of Palestinian prison stays, and can last up to three months.

Most Palestinians interviewed for the report said they were arrested overnight, blindfolded and handcuffed during transit. Thirty percent reported beatings before arriving at a detention facility. Once transferred to holding facilities, the report found "detainees were punched, kicked or beaten with rifle butts or clubs".

One-third of the Palestinians interviewed said they were imprisoned outdoors. "At night, four soldiers came and made us go out into the yard. It was cold and raining, and they made us take all our clothes off, strip completely naked," said Imad Abu Khalaf, 21.

Others were held indoors in solitary confinement between interrogation rounds. "The cell was full of cockroaches [and] very dirty," said Ibrahim Sabah, 19. "The blankets stank. After about 10 days, I had a rash all over my body. I scratched myself so much that I bled."

Researchers said many prisoners were tortured by the Palestinian Authority (PA) before arrest by Israeli authorities. Several were transferred directly from one agency to the next.

"Obviously the torture [in Israeli jails] is systematic," Jamal Dajani, director of strategic communications and media in the PA prime minister's office, told Al Jazeera. However, he said he was not aware of similar practices in Palestinian prisons: "I have no information where I can confirm these allegations."

The Israeli Ministry of Justice did not immediately respond to Al Jazeera's request for comment.

B'Tselem and HaMoked said there has been a lack of accountability for the mistreatment of detainees. Of more than 3,000 complaints filed with army prosecutors from September 2000 to the start of 2010, only 15 resulted in indictments for physical abuse, and of around 950 complaints made directly against Israel's interrogation agency from 2001 to 2015, all cases were closed without any formal investigation.

In September 2015, HaMoked filed a petition with Israel's high court to review the conditions in Shikma, and the court ruled in January that prison authorities must begin cleaning mattresses once a month and build walls between restrooms and sleeping areas.

More than 6,000 Palestinians are currently held in Israeli prisons throughout Israel and the occupied West Bank.