Pakistan on Tuesday hanged four militants involved in attacks on civilians, police and troops after they were convicted by the country’s controversial military courts, an army statement said.

It said the four, who were hanged at a prison in the northwestern province of Khyber Pakhtunkhwa, all belonged to the umbrella militant group Tehreek-e-Taliban Pakistan (TTP).

Pakistan’s powerful army chief last week confirmed death sentences passed by military courts on 30 militants, some of whom were involved in the country’s worst-ever extremist attack.

The assault on a school in Peshawar, the capital of Khyber Pakhtunkhwa, saw Taliban gunmen slaughter more than 150 people, the majority of them children.

The military courts — in which the army can try civilians on terror charges in secret, despite strong criticism from rights groups — were established in the wake of the 2014 attack, which traumatized a country already grimly accustomed to atrocities.

They were seen as an “exceptional” short-term measure to give the government time to reform the criminal justice system as the military targeted militants in the tribal areas of the northwest.

Security has dramatically improved since then. The law expired in January with the controversial tribunals having hanged 12 people and ordered the executions of 149 more.

But in February a fresh wave of militant violence killed 130 people across the country. Shortly afterwards, parliament voted to extend the courts for another two years.

Figures earlier this month showed 161 executions have been ordered by the courts since they were created and 24 of them have been carried out — not including Tuesday’s hangings.