The protests, led by PTI chief Imran Khan and fiery cleric Tahir ul-Qadri, erupted last month and descended into deadly confrontation on Saturday, with at least three people killed in clashes with police. Khan, who has refused to hold negotiations and says he would not call off protests until Sharif resigns, has called on his supporters to keep fighting.
Although they fired occasional teargas canisters, police were seen retreating and showing restraint as protesters, many carrying wooden clubs, pushed closer to Prime Minister Nawaz Sharif's official residence. It was not clear if he was at the residence.
Clashes in Islamabad as pressure mounts on PM to resign
Pakistani protesters wielding sticks and throwing stones clashed with police in the centre of the capital Islamabad on Monday after weeks of demonstrations demanding Prime Minister Nawaz Sharif's resignation turned violent over the weekend.
Despite heavy rain, crowds of protesters tried to break through police lines to push their way to the prime minister's residence. Police responded by firing teargas.
In a 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 talking to the protagonists and calling on them to show restraint.
Sharif, who swept to office last year in Pakistan's first democratic transition of power, has refused to resign. He is due to address both houses of parliament on Tuesday in an apparent effort to show that he is firmly in control.
Protestors heading towards PM House
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Pakistani Army had to intervene for defusing impasse
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Sharif ready to accept all demands except resignation
In a warning to police, the military said any further use of force to resolve an escalating political crisis would only worsen the situation. But it has also said the crisis had to be solved through talks, in a clear message to the protest leaders.
As protesters charged towards police lines in the so-called Red zone - home to the prime minister's house, parliament and many foreign embassies - security forces could be seen retreating, with police huddled in groups and avoiding direct confrontation.
Reflecting concern about security in the capital, all schools were closed on Monday, the start of a new academic year.
The protests, led by PTI chief Imran Khan and fiery cleric Tahir ul-Qadri, erupted last month and descended into deadly confrontation on Saturday, with at least three people killed in clashes with police.
Khan, who has refused to hold negotiations and says he would not call off protests until Sharif resigns, has called on his supporters to keep fighting.