ISLAMABAD — Pakistan executed two convicted terrorists Friday, the first of 400 militants headed to the hangman’s noose amid a government crackdown ordered after Taliban attackers gunned down 148 children and teachers Tuesday at a school in the northern city of Peshawar.

The sentences against Aqeel “Doctor Usman” and Arshad Mehmood were carried out at about 9 p.m. local time, behind closed doors at the prison in the eastern city of Faisalabad where they had been jailed.

Both were former soldiers convicted by court-martial. Their warrants of execution had been issued Thursday by the army chief of staff, Gen. Raheel Sharif, to show Pakistan’s zero-tolerance response to the school massacre.

Aqeel had been captured while leading an October 2009 raid on the army’s headquarters in Rawalpindi. Mehmood was involved in a December 2003 twin suicide car-bombing of the cavalcade of Gen. Pervez Musharraf, Pakistan’s military ruler at the time.

The government instructed jail administrators Friday to execute 20 other people on death row whose clemency appeals Musharraf had turned down while he held the dual office of president.

Those hangings will take place over the weekend and early next week, Interior Minister Nisar Ali Khan indicated.

The Ministry of Interior said its legal advisers were examining the case records of 378 convicted terrorists with a view to expediting their death sentences.

More than 3,000 convicted terrorists are imprisoned in Pakistan and will be executed in 2015, after Prime Minister Nawaz Sharif lifted a six-year moratorium on capital punishment Wednesday, which had been introduced by a previous administration.

The Pakistani Taliban vowed Friday to avenge the executions with attacks on the teenage children of army generals and politicians.

“We will avenge the death of each holy warrior by causing mourning in their homes,” it said in a statement e-mailed to journalists in Pakistan.

Security at the prisons was beefed up Friday after intelligence agencies warned of possible Taliban raids to free colleagues on death row.

However, the leader of the Pakistani Taliban, Maulana Fazlullah, has found himself increasingly isolated since ordering the attack on the Peshawar school.

Fazlullah is notorious for also ordering the October 2012 shooting of teenager Malala Yousafzai, the 2014 Nobel peace laureate.

Spokesmen for the Afghan Taliban and the biggest Pakistani Taliban breakaway faction, Jamaat-ul-Ahrar, have since issued statements condemning the killing of innocent schoolchildren and women.