The military said the 13 convicted militants sentenced Monday were involved in attacks on the armed forces, destruction of schools, and killing of innocent civilians.

"On the whole, they were involved in killing of 202 persons including 151 civilians, 51 Armed Forces/Frontier Constabulary/ Police Officials and injuring 249 others," according to an army statement.

It came after the military announced on August 16 that it had sentenced 15 militants to death.

The military courts allow the army to try civilians on terror charges in secret, despite strong criticism from rights groups.

They were established in the wake of a December 2014 Taliban massacre at an army-run school in Peshawar that killed over 150 people, mostly school children.

Following that attack the government lifted the moratorium on the death penalty. Scores of militants have since been condemned to death.

Excluding China, rights group Amnesty International says Iran, Saudi Arabia, Iraq and Pakistan -- in that order -- carried out 84 percent of all executions in 2017.

Activists say that the secret military trials violate rule of law and capital punishment after such trials denies right to life.

"Secret military trials of civilians that flout even basic fair trial guarantees are a blow to the rule of law and human rights," Reema Omer, a legal advisor at International Commission of Jurists (ICJ), told AFP

"The imposition of the death penalty after such trials violates the right to life, as according to the ICCPR (International Covenant on Civil and Political Rights), to which Pakistan is a party, proceedings in death penalty cases must must strictly comply with all fair trial rights," she added.

Pakistan has been fighting a homegrown Islamist insurgency since 2004, when militants displaced by the US-led invasion of Afghanistan began a campaign in border tribal areas.

Security has dramatically improved in the country in recent years.

But in April 2017, parliament voted to extend the courts for another two years.

Neither statement gave a date for the executions, but hangings have often been carried out within 24-48 hours in the past.