ISLAMABAD, Pakistan (CNN) -

The Pakistani military has waded into the political turmoil that has beset the civilian government in recent weeks, prompting concerns the country's fragile democracy could be undermined.

Demonstrations against the embattled government of Prime Minister Nawaz Sharif have been taking place in the capital, Islamabad, for the past two weeks.

The protests have brought together two opposition leaders who are calling for changes in government, but in different ways.

Imran Khan, the former cricket star who now leads one of Pakistan's largest political parties, has demanded the resignation of Sharif and new elections amid allegations of vote-rigging during last year's voting.

His supporters have joined with those of outspoken cleric Tahir ul Qadri, who says he wants an overhaul of Pakistan's political system. Qadri led demonstrations last year against the previous government, paralyzing the center of Islamabad.

After failing to negotiate a solution with the protest movements, Sharif on Thursday asked the country's powerful military for help brokering an end to the crisis.

'Deeper into the quicksand'

The decision is significant in a country ruled for long stretches by military dictators and where the Pakistani army has repeatedly intervened in the political process.

Bringing in the military "pushes democracy a little deeper into the quicksand where it had been trapped for many days," wrote The News International, a Pakistani newspaper, in an editorial Friday. "Whether it can pull itself out remains an open question."

Sharif clashed with the military when he served as prime minister during the 1990s, resulting in a lengthy period of exile before his return to power last year.

Both Khan and Qadri met late Thursday with the army chief, Gen. Raheel Sharif, who is not related to the prime minister.

The two leaders have separately threatened to let their protesters storm parliament if their demands are not. The demonstrators have been camped out in an area of the capital where many key state institutions are based.

Anger over shooting

The Qadri-led protests have been fueled by anger over the fatal shooting of at least 10 of his supporters by police in the city of Lahore in June. Qadri has alleged that Shahbaz Sharif, the chief minister of Punjab province and the brother of the prime minister, was ultimately responsible for the shooting.

Lahore police registered a report Thursday that listed the two Sharif brothers, as well as other top officials, as suspects in the shooting case. The move doesn't amount to formal charges against the suspects.

It was widely seen as an effort to placate Qadri and his supporters, but the cleric said it didn't go far enough. He called for the resignation of Shahbaz Sharif and the registering of a new report based on his movement's allegations.

The turbulence has put pressure on Pakistan's political system, which last year carried out a transition from one democratically elected government to another for the first time in its history. Sharif's government has been in power for less than 15 months.

Commenting on the current crisis Thursday, U.S. State Department Spokeswoman Jen Psaki said, "We continue to urge all sides to refrain from violence, exercise restraint, respect the rule of law."