The human rights group said in a report abuses in the North Eastern Province of Kenya included rape and attempted sexual assault, beatings and other physical mistreatment, arbitrary detention, extortion, looting and destruction of property as well as inhumane treatment such as forcing victims to sit in water or roll on the ground.
The Kenyan government has said it would investigate but no police or soldiers have been charged, disciplined or "otherwise held accountable," HRW said in a news release.
The abuses, HRW said, were apparently in response to grenade and improvised-explosive device attacks targeting security forces and civilians in the North Eastern Province.
"The attacks carried out by suspected al-Shabaab supporters are abhorrent, but they can never justify this kind of indiscriminate abuse," Leslie Lefkow, deputy Africa director at Human Rights Watch, said in the news release. "Kenyan police and soldiers ought to be protecting civilians, not assaulting them."
The most serious abuses were by police in the Dadaab refugee camps, with more than 466,000 refugees, mostly Somali, where HRW said women were sexually assaulted and children as young as 4 years old were beaten.
Since February, HRW said, there have been no major attacks by militants in the North Eastern Province, and abuses have subsided.
But the human rights group said a member of Kenyan Parliament interviewed by HRW said: "The war will likely continue, and [the security forces] need to avoid responding like this again. ... They cannot correct a wrong with a wrong."
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