Demonstrators led by opposition leaders Imran Khan, a hero cricket player turned politician, and Tahir ul-Qadri, a firebrand cleric, have been on the streets for weeks trying to bring down the government of prime minister Nawaz Sharif.
The protests descended into deadly chaos at the weekend as demonstrators clashed with police in a central area near many government buildings and embassies. Three people were killed.
Mr Sharif, who was toppled by the army in a 1999 coup but resumed power after his party won elections in 2013, has refused to quit, while protest leaders have rejected his offer of talks, creating a dangerous deadlock.
Clashes broke out again early yesterday, and the PTV channel and its English-language service, PTV World, were taken off the air after protesters stormed its headquarters.
A PTV source said the activists had occupied the main control room and smashed some equipment. Television pictures showed uniformed members of a paramilitary force and soldiers walking calmly into the building. Witnesses said the soldiers escorted protesters out and put the building under their protection.
There were no signs of violence and the protesters were seen leaving peacefully. The station later went back on air.
In the nuclear-armed nation, where power has often changed hands through military coups rather than elections, the army is bound to play a key role in how the conflict unfolds, but it has not directly intervened, apart from meeting the protagonists and calling on them to show restraint.
Army chief General Raheel Sharif met the prime minister yesterday, but it was unclear what they discussed.
The army chief, who is not related to Mr Sharif, had on Sunday urged the government and opposition leaders to resolve the crisis through talks and warned against the use of force to end the demonstrations.
Protesters have camped out in Islamabad since mid-August, paralysing life in the centre of the capital and creating massive traffic jams. The protest site, where many sleep rough every night, is littered with rubbish and reeks of human waste.
How the crisis ends will ultimately be decided by the army. If the protests get out of hand, the military could step in decisively, imposing a curfew or even martial law.
There is also a question mark over the extent to which protest leaders are capable of controlling their own people, many of whom are frustrated after weeks of hardship and with no solution in sight.
Alternatively, the army could side with the protesters and put pressure on Mr Sharif to resign, in which case an interim administration would have to be put in place and early parliamentary elections held to elect a new government.
However, few observers believe the army is bent on seizing power again.
A weakened Mr Sharif would allow the army to remain firmly in charge of key issues such as relations with India and Afghanistan, while allowing the civilian government to deal with day-to-day economic problems in which it has little interest. Some ruling party officials have accused elements within the military of orchestrating the protests to weaken the government.
Mr Khan and Mr Qadri have instructed their supporters to avoid any confrontation with the armed forces and to strictly follow their orders. As soldiers entered the PTV building yesterday, many protesters smiled and shook hands with them.
The military insists it does not meddle in politics, but it was known to be frustrated with the government, in particular over the treason trial of former military chief and ex-president Pervez Musharraf, who deposed Mr Sharif in 1999.