Here's the latest developments in this story:
A second round of talks between Mr Khan's party and the government was to take place today. For the first round of talks in Islamabad's Mariott Hotel in the early hours of Thursday, Mr Khan had sent a negotiating team, headed by former Foreign Minister Shah Mehmood Qureshi, while he continued to picket the capital's Red Zone, which houses key buildings including Parliament, the prime minister's house and numerous Western embassies.
The PTI announced that it was suspending talks just before Mr Khan addressed his supporters from the top of a shipping container outside parliament on Thursday, slamming the government for reportedly removing Inspector General of Police (IGP) Islamabad Aftab Cheema.
Amid speculation that Mr Cheema was removed today because he had refused to attack protesters, Imran Khan warned the police against action on people picketing the Red Zone. "If bullets are fired, I will stand in their way," he said.
Mr Khan and Tahir-ul Qadri, a cleric who has joined his protest, the 'Azadi march', claim that last year's general election - in which Mr Sharif's Pakistan Muslim League - Nawaz or PML-N won a landslide victory - was rigged and so the PM must resign. The election was rated as free and credible by international observers.
Mr Khan also wants the PM's brother and Punjab Chief Minister Shahbaz Sharif to resign; he wants an interim government installed while his rigging charges are probed; he wants electoral reforms before fresh elections; re-elections for all assemblies; he wants responsibility fixed for the alleged rigging of last year's national election and an audit of government expenses. (Imran Khan's Party Hands Six Demands to Government Negotiators)
Mr Sharif has refused to resign. He attended Parliament today; his daughter Maryam Nawaz Sharif tweeted a picture of him smiling and said, "The peace and calm and smile to die for ! :) PM looks unperturbed !"
The peace and calm and smile to die for ! :) PM looks unperturbed ! pic.twitter.com/qY8voTumfE
- Maryam Nawaz Sharif (@MaryamNSharif) August 21, 2014On Thursday, the lower house of parliament passed a unanimous resolution rejecting calls for Mr Sharif's resignation and vowing to uphold democracy. (Read)
Mr Khan and Mr Qadri were summoned today by a three-member bench of the Supreme Court, which is investigating Mr Khan's allegation that the national elections held last year were rigged.
Last evening, a deadline set by Imran Khan for Mr Sharif's resignation passed without the former cricketer carrying out his threat of storming the Prime Minister's residence. "I thought I would take you all to the Prime Minister's house today. (But) his heart is already in bad shape. If I ask my followers to go in that direction and he has heart attack - I cannot do that," he said.
Nuclear-armed Pakistan has experienced three military coups and Mr Khan's protest raises fears of the army stepping in. Thus, opposition parties had shunned Mr Khan's call to unseat the government and urged him to come to the negotiating table. (Also read: Pakistan Social Media Abuzz with Pro and Anti-Government Debates)
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