A Pakistani law allowing secret military courts to try civilians on terror charges expired Saturday, after the controversial tribunals hanged 12 people and ordered the executions of 149 more amid sharp criticism from rights groups.

The government has not said whether it plans to extend use of the courts, created by constitutional amendment after the country's deadliest ever extremist attack in 2014.

The assault on a school in northwestern Peshawar, in which gunmen killed more than 150 people -- mostly children -- traumatised a country already grimly accustomed to atrocities.

The army intensified an operation against militants in the tribal areas and the government launched a National Action Plan, including the creation of the courts, against extremism.

The courts were seen as an "exceptional" short-term measure put in place to allow the government time to reform the criminal justice system.

But rights activists called for greater transparency, saying the courts failed to meet even the murky standards of military tribunals around the world.

In a statement issued to the media Friday, the International Commission of Jurists (ICJ) said justice reform had not been carried out, and called for fair, credible trials.

"The lapse of the jurisdiction of military courts over civilians is a step in the right direction, but unsurprisingly, there is no sign of the promised reforms to strengthen the ordinary criminal justice system to effectively handle terrorism-related cases," said Sam Zarifi, ICJ's Asia Director.

"The Pakistani Government must not re-enact legislation to continue secret military trials of civilians, nor resort to more short-term, short-sighted security measures that are contrary to human rights protections," Zarifi added.

Analyst Imtiaz Gul said heavy criticism meant Pakistan was unlikely to extend the courts, saying the controversy had been an "embarrassment" to the country.

Quoting military sources, the ICJ said 274 people have been convicted by military courts since January 2015, of which 161 have been sentenced to death. Twelve of those have already been hanged.

The rights group said the details of only seven cases where people were given life imprisonment have been made public.

"The names, charges, and duration of prison terms for the remaining 106 people have not been disclosed," ICJ said.