ISLAMABAD: Thousands of Pakistanis fed up with a government they say is corrupt and indifferent to the plight of common citizens descended on the capital Monday, responding to the call of a charismatic cleric who has quickly become a powerful but mysterious political force.

The dramatic entry into Pakistani politics of Tahir-ul-Qadri, a preacher who until recently lived in Canada, has sparked concern from some that he is seeking to derail elections expected this spring at the behest of the powerful army.

Qadri has denied those allegations and insisted his vaguely worded demands for election reform are simply meant to root out corruption in the political system. He pledged several weeks ago to lead a "million-man march" on Islamabad on Monday to press his demands.

The turnout appeared to fall far short of Qadri's promise, but there was no lack of enthusiasm from the crowd. Many waved green and white Pakistani flags and wore buttons emblazoned with the cleric's picture. Although some spoke of election reform, most were focused on demands like fixing the country's rampant energy shortages and rooting out corruption.

"There is no electricity and no gas, and the government has done nothing," said Faizan Baig, a 23-year-old pharmaceutical company worker who traveled to Islamabad from the northwest town of Abbottabad. "Qadri feels pain for the people, while the government feels no pain for the people."

Baig was among about 10,000 people who streamed into the capital throughout the day Monday and camped out on the main avenue running through the city. Male protesters gathered on one side of the road while women and children were on the other, divided by a grass median.

Qadri left his home base in the eastern city of Lahore on Sunday accompanied by at least 15,000 people in hundreds of vehicles, but he had not yet arrived in Islamabad by Monday evening. The numbers were expected to grow as the procession reached the capital, and Qadri's spokesman, Shahid Mursaleen, claimed they still planned to deliver a massive crowd.

But Pakistani Interior Minister Rehman Malik, who has not hidden his disdain for Qadri, estimated the total crowd in Islamabad would not exceed 25,000.

The government set up dozens of shipping containers in the capital to prevent protesters from reaching key government areas. Thousands of paramilitary forces and police in riot gear were also deployed throughout the city and cell phones were jammed after the government warned that militants were planning to attack the protesters.

The demonstrators established a make-shift stage on top of one of the shipping containers set up by the government, and people took turns delivering fiery speeches extolling Qadri. Helicopters providing security buzzed low overhead to the delight of the protesters, who waved their flags and cheered.

"I have responded to the call of our leader for a revolution," said Mohammed Aslam, a 52-year-old farmer who traveled from the central Pakistani city of Sargodha. "The country's leaders usually ignore the voice of the poor, but I think this event may change that."

Qadri returned to Pakistan in December after years in Canada, where he's also a citizen. He heads a religious network in Lahore and gained some international prominence by writing a 2010 fatwa, or religious opinion, condemning terrorism.

But he was never a national political figure until this winter, when his calls for reforms ahead of elections galvanized many Pakistanis disenchanted by the existing parties. The cleric's vaguely worded demands include vetting of political candidates to make sure they're honest and taking steps to even out the playing field so more people can participate in the political process.

Qadri has pledged that he and his supporters will remain in Islamabad until their demands are met, and many brought food and blankets with them so they could hunker down. That could set up a clash with the government.

Some of Qadri's comments have sparked concern that the cleric is a front for the Pakistani military to disrupt the democratic process just as it prepares for a historic transfer of power from one civilian government to another.

He has called for a military role in picking the caretaker government that will take over temporarily ahead of elections and has said it could stay in place longer than normal to enact necessary reforms.

Those comments, as well as questions about where his funding is coming from, have sparked fears Qadri is really trying to derail the upcoming vote on behalf of the military, which is believed to dislike both the main political parties vying for power, and pave the way for a military-backed caretaker to hold power indefinitely. Qadri has denied any such involvement.