LONDON, United Kingdom (AFP)— UK counter-terror police are leading an investigation into the jailed plotter of the deadly 2017 Manchester bombing after he was accused of throwing hot oil over prison guards and attacking them with makeshift weapons.

Hashem Abedi — who is serving a life sentence over the bombing that killed 22 people at an Ariana Grande concert — threw the cooking oil over three officers on Saturday before stabbing them with “home-made weapons,” according to the Prison Officers’ Association trade union.

Two of the officers at the prison near Durham, northern England, remain in hospital with serious injuries, while a third has been discharged, police said.

“An investigation is underway following a serious assault which occurred at HMP Frankland in Durham today,” counter-terror police in northeast England said on Saturday. “The suspect has been detained.”

In May 2017 Hashem’s brother Salman Abedi detonated a homemade suicide bomb at the pop concert in Manchester Arena, targeting crowds of mostly young people.

Hashem was jailed for life with a minimum term of 55 years for playing an “integral part” in the attack, which was inspired by the Islamic State group.

Britain’s Justice Secretary Shabana Mahmood said she was “appalled” by the attack on the prison guards.

“I will be pushing for the strongest possible punishment,” she said on social media on Saturday. “Violence against our staff will never be tolerated.”