Hamas prisoners stabbed two guards at the Ketziot prison in southern Israel on Sunday, injuring one of them seriously, according to prison services. The attack sparked a riot in which 11 inmates were also reported hurt.

The badly wounded guard sustained stab wounds to the neck, while the second, lightly hurt officer had a hand injury. The guards were airlifted to the nearby Soroka Medical Center in Beersheba for treatment.

The hospital later said the condition of the guard had stabilized and he was listed in a moderate condition.

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According to Hebrew reports, the guards were attacked with improvised weapons fashioned into knives. The riot came as security prisoners were being moved between cells. The attack came as part of an ongoing effort by Israel to restrict cellphone usage by the prisoners, including the installation of jamming systems.

Eleven prisoners were also injured and hospitalized after security forces quelled the riot. Seven of the prisoners were also airlifted to hospital by the IDF, the Haaretz daily reported. Their condition was not immediately clear, with the Israel Prison Service saying they were “in various conditions.”

The prison service said the situation was under control, but gave no details on how it put down the riot.

The incident came a week after Hamas prisoners in the Ramon prison torched 14 beds, setting a fire in the wing.

The blaze was quickly extinguished and no injuries were reported. In that incident too, prisoners were protesting restrictions on cellphone usage.

Public Security Minister Gilad Erdan said the attack “was very serious and proves once again that the prisons service is on the front-line of the war against terror.”

Erdan vowed the jamming would continue, saying that blocking their ability to use mobile phones was an important step in attempts to prevent “terror attacks being directed from within the prison against Israeli civilians.”