Pakistan's major opposition parties expressed scepticism on Tuesday about the government's proposal to revive special military courts to try civilians charged with terrorism, potentially jeopardising a proposed constitutional amendment.

Prime Minister Nawaz Sharif's office said on Monday that it would seek to keep military courts in place, days after the secret tribunals' original legal mandate had expired.

However, the ruling Pakistan Muslim League-Nawaz (PML-N) party does not have the two-thirds National Assembly majority necessary to amend the constitution, meaning it would need support from at least some opposition lawmakers. That is likely to be a hard sell.

“We are against any extension for military courts,” Senator Saeed Ghani of the leading opposition Pakistan People's Party (PPP) told Reuters.

He asked what the government had done to improve civilian courts during the military tribunal's two-year mandate, noting that the original justification for the special courts was to allow time for reforms.

Military courts in Pakistan have been accused of fostering human rights abuses and criticised for a lack of transparency and accountability.

A spokesman for the other main opposition party, the Pakistan Tehreek-i-Insaf (PTI), criticised the courts as undemocratic but said it would hear out the government's plans.

“We have asked the government to tell us what reforms have been made to the (civilian) anti-terrorism courts,” said Fawad Chaudhry. “But we have not taken a final decision.”

PML-N has 189 seats in the 342 member National Assembly, falling short by 39 votes.

Swaying the PTI, which has 33 assembly seats, to vote for reinstating the military courts would be a major achievement.

The two parties have been at loggerheads over corruption allegations levelled at Nawaz after his children's names appeared in the Panama Papers as owners of offshore companies.

Military trials of terrorism suspects were legalised in January 2015 with lawmakers and the military arguing that civilian courts were unable to process cases swiftly because many judges feared becoming victims of revenge attacks.

The courts have since delivered 275 convictions, including 161 death sentences, and carried out 12 executions. These courts do not allow the right to appeal and judges are not required to have law degrees or provide reasons for their verdicts.

The government has called for a conference on Jan 17 to discuss the issue.

Both opposition parties said they would attend the meeting but PPP's Ghani added: “It is unlikely that there will be a change in our stance.”