One of Pakistan's best-known religious parties has come under unprecedented criticism from the country's army after its leader declared a Taliban chief a revered "martyr" following his killing by a US drone this month.

Jamaat-e-Islami (JI), South Asia's oldest Islamist party, has been buffeted by a torrent of criticism from the media and political rivals after the head of the party, Munawar Hassan, declared the Pakistani Taliban leader Hakimullah Mehsud a shaheed after he was killed.

But the decision by the country's much-respected army to blast Hassan over his language is seen by some analysts as a weakening of the "mullah-military alliance" that has endured between JI and the army for decades.

Hassan's remarks on a television programme, during which he also said Pakistani troops killed while supporting the US conflict with the Taliban should not be considered martyrs, were described in an official army statement as "painful and unfortunate".

The statement read: "The people of Pakistan, whose loved ones laid down their life while fighting the terrorists, and families of shuhada [martyrs], of armed forces, demand an unconditional apology from Syed Munawar Hassan for hurting their feelings."

However, the party has dug in its heels and refused to apologise, saying the army was guilty of interfering in politics.

Hassan made his comments in the wake of a national controversy over the death of Mehsud, the hardline chief of the Tehrik-e-Taliban Pakistan, who was killed by a US drone on 1 November. Although Mehsud was hated by most Pakistanis, US drones are also widely reviled, leading to a confused response to his killing.

"It's a major turning point for the army," said Raza Rumi, director of the Jinnah Institute thinktank. "The alliance [between the army and JI] has been there for 45 years and this is the first time the army has issued such a clear, unequivocal rebuke."

While JI and other Islamist parties have always called for pure Islamic law to be introduced in Pakistan, they have remained inside the political system. The party has a handful of seats in the national assembly and is the coalition partner with Imran Khan in government in the provincial assembly of Khyber Pakhtunkhwa.

But increasingly the religious parties have been pushed to the right as they feel they must appeal to the most extreme elements of society.

Rumi said: "In calling a man a martyr who was struggling to overthrow the state, it means we have now passed the point where Islamist parties could drum some sense into violent extremists. They are now so powerful even mainstream Islamist parties are afraid of them."

Another major religious party, a faction of the Jamiat Ulema-e-Islam led by Maulana Fazlur Rehman, also sparked anger in the wake of the killing of Mehsud by claiming anyone, "even a dog", who is killed by the US should be considered a martyr.

The statements by both leaders have stirred up intense criticism. On Monday the Sunni Ittehad Council, an umbrella group representing followers of the moderate Barelvi school of Islam, demanded Hassan be tried for treason.

The army's reprimand is regarded as remarkable, given JI's support for all three military dictators who have seized power during Pakistan's history. It also helped supply militants to fight the state-backed insurgency in Indian-occupied Kashmir in the 1990s.

That closeness has enabled the party to ride out embarrassing controversies in the past, including evidence that senior party leaders had close links to al-Qaida.

In 2003 Khalid Sheikh Mohammad, the mastermind of the 9/11 plot, was found hiding in the house of local JI leader .