JALALABAD, Afghanistan (Reuters) - Militants from Islamic State have beheaded three brothers, all working in the medical profession, in Afghanistan’s eastern province of Nangarhar, an official said on Monday.

Attaullah Khogyani, spokesman for the governor of Nangarhar, the main stronghold of Islamic State in Afghanistan, said the brothers were killed in Chaparhar district on Saturday night.

The eldest brother Nisar Tareliwal, 27, was a doctor at a private clinic, the middle brother Nayeem, 24, was working as a vaccine campaigner and the youngest Abdul Wahab, 19, was a medical student.

Khogyani said the father of the victims, a doctor was beheaded last year by the Islamic State, which has acquired a reputation for brutality in the province, beheading prisoners on a number of occasions.

In a separate incident the Islamic State kidnapped 11 farmers in Rodat district of Nangarhar province, although they later released two of them.

There was no claim by Islamic State about the two incidents.

Nangarhar, on the porous border with Pakistan, has become a stronghold for Islamic State, generally known as Daesh in Afghanistan, which has grown to become one of the country’s most dangerous militant groups since it appeared around the start of 2015.

Lal Mohammed Durrani, deputy chairman of the provincial council in Nangarhar, said the abduction took place when the farmers were working in poppy fields.

The process to harvest poppy crop has kicked off in provinces across Afghanistan, the world’s top opium producer.

Last year the U.N. Office on Drugs and Crime (UNODC) said output of opium made from poppy seeds in Afghanistan, the world’s main source of heroin, stood at around 9,000 metric tons.

The illicit drug has fueled insecurity, violence and insurgency in Afghanistan for several decades.