A controversial law in Pakistan that allowed military courts to try people on "terrorism" charges has expired, two years after its introduction following an attack that left scores of schoolchildren dead.

During their time of existence, the tribunals hanged 12 people and ordered the executions of 149 more amid sharp criticism from rights groups.

The courts were set up in the wake of a 2014 assault on a school in northwestern Peshawar, in which gunmen killed at least 141 people , mostly children.

"The two-year term of military courts will be completed today," finance minister Ishaq Dar told a press conference on Saturday.

"The government has not taken any decision on their renewal so far."

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Following the Peshawar attack, claimed by the Pakistani Taliban, also known as Tahreek-e-Taliban, the army intensified an operation against armed groups in the tribal areas and the government launched a National Action Plan, including the creation of the courts.

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

Their establishment prompted concern from human rights activists and was even challenged in the country's top court by a group of lawyers in April 2015.

Rights activists also 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 on Friday, the International Commission of Jurists (ICJ) said justice reform had not been carried out, and called for fair, credible trials.

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"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 told AFP news agency that 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.

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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.

On Friday, local media quoted Chaudhry Nisar Ali Khan, interior minister, saying that, from now on, the cases which were sent to the military courts will be referred to existing anti-terrorism courts.