A fiery anti-government cleric is leading a massive really in Pakistan's capital, demanding the country's prime minister step down over alleged fraud in last year's election.

Tahir-ul-Qadri, along with famous cricketer-turned politician Imran Khan, are leading tens of thousands to protest in Islamabad. They want Prime Minister Nawaz Sharif to step down over alleged fraud in the country's May 2013 election.

Sharif has said he won't step down, raising fears of possible political instability in this nuclear-armed country.

On Saturday, Qadri told his supporters to continue protesting until they bring a "peaceful revolution." Khan's supporters have camped out nearby.

Both Khan and Qadri have vowed to bring 1 million followers into the streets of Islamabad, a city of roughly 1.7 million inhabitants.