* Protests demanding PM resignation started in mid-August
* How crisis unfolds depends on army's actions
* Protesters clash with police, advance on PM house (Adds detail, comment from Khan)
By Syed Raza Hassan and Maria Golovnina
ISLAMABAD, Sept 1 (Reuters) - Pakistani protesters wielding sticks and throwing stones marched on government buildings in the capital Islamabad on Monday after weeks of demonstrations demanding Prime Minister Nawaz Sharif's resignation turned violent over the weekend.
Protests led by Imran Khan, a renowned cricketer before entering politics, and fiery cleric Tahir ul-Qadri, erupted last month and descended into deadly chaos on Saturday, with at least three people killed in clashes with police.
On Monday morning, despite heavy rain, crowds of protesters fought running battles with retreating police forces after breaking the main gate into the Pakistan Secretariat area which houses government ministries as well as Sharif's residence.
Although they fired occasional teargas canisters, police were seen retreating and showing restraint as protesters, many carrying wooden clubs, pushed closer to Sharif's house. It was not clear if he was at the residence.
The protesters, many of them visibly angry, could be seen beating motorcycles and cars with their sticks as they advanced closer to their target. They had tried to storm Sharif's house on Saturday night but were beaten back by police.
The head of Islamabad police and another senior police officer were lightly wounded in the clashes, media reported.
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.
But Sharif looks increasingly cornered in the conflict, and even if he survives the crisis he is likely to remain significantly weakened for the rest of his tenure and sidelined by the army on key issues such as foreign policy and security.
The protesters out on Monday appeared to be from Qadri's camp, with Khan, who has refused to hold negotiations and says he would not call off the protests until Sharif resigns, calling on his people to avoid any form of violence.
"I call upon my workers to remain peaceful," he said from atop a shipping container at the main rally site. "Do not carry out any acts of violence. God has given us victory."
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 Khan and Qadri.
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. (Writing by Maria Golovnina)
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