Pakistan's politicians have rallied behind the country's embattled prime minister during a meeting of parliament convened amid violent street protests that some claim have been secretly backed by the country's powerful army.

Senior politicians took turns on Tuesday to promise to defend the democratic system against protesters who are demanding the resignation of the prime minister, Nawaz Sharif, just 15 months after he was elected.

The interior minister, Chaudhry Nisar, described the demonstrations led by former cricket star Imran Khan and populist cleric Tahir-ul-Qadri as a "revolt against the state".

In recent days the weeks-long crisis has deepened. The state-run broadcaster was briefly forced off air, deadly fights broke out with police on the streets of Islamabad and the perimeter fence of parliament was smashed, allowing protesters to set up a camp on the building's lawns.

But it was not just the hostile crowds directly outside the chamber of the national assembly that concerned speakers during the debate.

The role of the army, which has ruled directly and through weak civilian governments for most of the country's history, was also openly questioned.

Speaking to the joint session of Pakistan's two houses of parliament, Fazal-ur-Rehman, the head of a major religious party, criticised the army's behaviour during the crisis, which he said had created the impression protesters had been "backed by a third party".

Newspapers have been more direct in their criticism of any army which has strenuously avoided riding to the government's rescue.

Dawn, a leading English language daily, expressed outrage that the army instructed the government on Sunday not to use force against rioters attacking state buildings: "It's as if the army is unaware – rather, unwilling – to acknowledge the constitutional scheme of things: it is the government that is supposed to give orders to the army, not the other way around."

The Nation said it "should be simply unacceptable" for military commanders to tell elected politicians what to do.

Many Pakistanis are convinced the army has stage-managed protests ostensibly led by two civilians: Imran Khan and Tahir-ul-Qadri.

Both men, playing on widespread dissatisfaction with a democratic system that many believe only serves a corrupt political class, launched demonstrations on 14 August intended to try and force out the government. Qadri has called for a "Green Revolution" while Khan has demanded the sacking of Sharif and a rerun of last year's election. He claims massive election rigging robbed him of power, but no independent observer group says fraud was widespread enough to change the landslide win for Sharif, leader of his own faction of the Pakistan Muslim League.

Although both men insist their movements are peaceful, they have used language certain to incite crowds which have varied from between just a few thousand up to an estimated 50,000.

Things finally turned violent on Saturday when Khan and Qadri gave the order to try and seize the prime minister's official residence, triggering clashes that left three dead and injured hundreds. On Monday they launched an early morning raid on the headquarters of the Pakistan Television Corporation (PTV), which they successful occupied.

But protesters, who have viciously attacked policemen in recent days, calmly left PTV when asked to do so by military men who they believe will eventually force Sharif out.

In his many speeches over the last fortnight Khan has frequently promised a "third umpire" would send Sharif packing.

Adding to fears of a military-backed plot, Javed Hashmi, president of Khan's Pakistan Tehreek-e-Insaf, parted ways with Khan after dramatically claiming the party leader had been acting under the directions of the army throughout.

Neither Hashmi nor anyone else has offered hard evidence to back up claims of a military plot to subvert democracy, although relations between the army and Sharif have been terrible in all three of his terms in office.

His most recent stint has been no different, with the army antagonised by Sharif's efforts to firmly establish civilian supremacy over the army, not least with a historic – and provocative – high treason trial of Pervez Musharraf, the military ruler who ousted Sharif in 1999.

Not everyone is convinced the chaotic events of recent days are really the result of a carefully plotted script.

"People are stuck in old paradigms as if this was still the 1980s or 90s," said Kamran Bokhari an analyst at Stratfor, a private intelligence firm.

"They treat the armed forces as a sort of all powerful, omnipotent monolith that has been completely unchanged by all the many other changes in Pakistan over the decades."

The army may well have grabbed the opportunity created by the crisis to clip Sharif's wings, Bokhari believes.

But it is unlikely to have full control of Khan, whose behaviour has at times appeared impetuous. If anything, Khan might believe he can force the army to do what he wants.

Hasan Askari Rizvi, a Lahore-based political scientist, said the army's room to manoeuvre has been steadily reduced by the emergence of rival power centres over the past decade.

Those include everything from a burgeoning media sector to militant groups such as the Taliban, as well as parliament itself, which on Tuesday put on a powerful display of unity.

"The problem for the army is that Pakistan has changed over the last seven years," said Rizvi. "It's still the most powerful institution but it has to work under new constraints."