At least eight people were killed and 13 others injured in two explosions at notorious Insein Prison in Yangon on Wednesday morning, according to prison sources. Those killed included three prison staff and relatives of political prisoners.

According to a prison staffer who wished to remain anonymous, two bombs exploded in a building near the prison entrance used for receiving supplies bought for inmates by relatives. Three prison staff died of injuries from the blasts.

“Some people who were delivering food for inmates were also hit,” said the prison source.  All five others killed were reportedly women, according to witnesses. “We heard loud explosions, and saw five female visitors dead, and some 13 others were injured,” said a witness.

Among those killed were Daw Kyee Myint, the mother of the prominent imprisoned student activist Ko Lin Htet Naing, also known as Ko James.

“His mother went to the prison to deliver food for her son as there was his trial today,” a relative of Ko Lin Htet Aung told DMG. “We phoned her several times after we heard about the blasts. But we couldn’t get through, and when we enquired, we were able to confirm that she died in the explosions.”

Ko Lin Htet Aung is a former member of the All Burma Federation of Student Unions (ABFSU). He was arrested in June in Yangon, and faces incitement charges before a junta-controlled court in Insein Prison.

It was not immediately clear which group was responsible for the blasts, and no group had yet claimed responsibility as of press time. The regime tightened security in and around the Yangon prison after Wednesday’s blasts.

The neighbourhood surrounding Insein Prison and the prison staff-quarters have been frequently targeted since June, and at least five prison staffers were injured in previous explosions.