A Pakistani-Canadian cleric who is leading the campaign to topple the government in his native country said Tuesday he will continue his fight despite a murder investigation launched against him by Pakistani police.

Muhammad Tahir-ul-Qadri, who left Toronto in June to return to his hometown of Lahore, has called on thousands of his supporters to march on the capital Islamabad on Thursday in a bid to oust the government of Prime Minister Nawaz Sharif.

Police in Lahore launched a murder investigation against Qadri on Sunday after authorities said an officer died during clashes with his supporters. Police allege the cleric incited people to violence, but Qadri denied the allegations.

"All cases are just fabricated, just fabricated, based on false accusations," he told The Canadian Press in a telephone interview from Lahore.

The protests planned for Thursday -- the country's independence day -- represent the strongest challenge yet to Sharif's government, just a year after he took office in the first democratic transfer of power in a country long plagued by military coups.

Qadri has a loyal following of thousands through his network of mosques and religious schools in Pakistan. He is the founder of Minhaj-ul-Quran International, a liberal Islamic group that promotes peace and interfaith dialogue.

The 63-year-old cleric first held a protest in Islamabad last year, calling for election reforms ahead of the country's May poll.

There has been wide speculation that Qadri has internal support from Pakistan's powerful military, whose relation with Sharif's government has been strained over its refusal to allow former president Pervez Musharraf leave the country, but Qadri says that's not true.

"I have never met a single general and I have never spoken to any general on telephone even. I have no contact. This is totally a lie. I reject it," he said, adding that it's in the "culture of Pakistani politics" to make false allegations against those who raise their voice against the government.

Qadri said he is fighting for justice and democracy, accusing the government of widespread corruption, use of police for political purposes and violation of basic freedoms.

"We're raising a democratic voice just to get the basic rights of human beings," he said.

Qadri said he is outraged over the killing of 14 party workers during a standoff with police in June. He said two months have passed and a police investigation has yet to be launched.

"Is this democracy? Is this the system of protection of human life? Is this the system of justice?"

Prof. Madiha Afzal, an expert on Pakistan affairs at Brookings Institution in Washington, said Qadri's influence in the anti-government movement is limited as he's not an elected politician.

"But the forceful and ultimately fatal way in which the government dealt with his supporters in June in Lahore, and the violent interaction again this past week has lent him greater legitimacy," she said in an email.

The Pakistani government has dismissed Thursday's march as simply chaos created by "Musharraf's friends," but authorities are taking no chances.

Shipping containers blocked many roads leading into central Islamabad on Tuesday and police in riot gear could be seen taking up positions across the city as authorities suspended mobile phone service in some areas.

The government has also invoked a rarely-used article in the constitution allowing the military to step in to maintain law and order if needed.

Qadri said the Lahore suburb of Model Town, where he lives, has been under a virtual siege for the past 10 days as part of a government security clampdown.

"Absolute blockade for the last 10 days. We're in a jail, like in Gaza."

A Foreign Affairs spokesman in Ottawa said the department was aware of media reports about the investigation against Qadri and it was monitoring the situation, but refused to comment further, citing privacy reasons.

Qadri said he has had no contact with the Canadian government.