Sixteen prisoners were secretly hanged at Mashhad’s Vakilabad Prison on May 23 and 24, says the International Campaign for Human Rights in Iran, citing “reliable sources.”

It reports that on May 23, twelve prisoners were hanged for drug charges. The next day, three sisters were hanged for drug charges and a convicted rapist was executed.

The International Campaign for Human Rights in Iran had earlier reported that over the past two and a half months, 70 prisoners have been hanged in Vakilabad Prison. The campaign contends that the executions were drug related and carried out secretly and en masse.

The campaign maintains that the prisoners were executed without prior notification to the families and lawyers of the prisoners.

The recent surge in the number of executions in Iran has set off alarm bells in international human rights communities.

In March, UN Secretary General Ban Ki-moon expressed “international concern” regarding the rise in executions in Iran and the conditions of prisoners at Mashhad’s Vakilabad Prison in particular.