ISLAMABAD — Pakistani police fired tear gas at thousands of protesters as they tried to march toward the prime minister’s home in the capital on Saturday, blanketing the route with clouds of white smoke and scattering demonstrators.

Police also fired rubber bullets to disperse the crowd, injuring some protesters, and at least a dozen were taken to a hospital.

The march’s leaders, including cricket-legend-turned politician Imran Khan and anti-government cleric Tahirul Qadri, called for the demonstration to move to the house from separate massive rallies in front of the parliament, where they have been staging a sit-in for days. Some 20,000 police in riot gear are there to block the procession.

In speeches, Khan and Qadri say they will remain peaceful and urged security forces to abstain from using force against the protesters.

The two allege that Prime Minister Nawaz Sharif won the 2013 election due to massive voter fraud. They demand he step down but Sharif has refused.

Both Khan and Qadri, a dual Pakistani-Canadian citizen with a wide following, also demand reforms in Pakistan’s electoral system to prevent future voter fraud.

Backed by parliament and many political parties, Sharif has said he will not step down. Government negotiators are trying to convince Qadri and Khan to end their protest and abandon the demand for Sharif’s resignation.

The demonstration began with a march from the eastern city of Lahore on the country’s Independence Day, Aug. 14. Khan and Qadri had called for millions protesters to join but crowds have not been more than tens of thousands.

The protesters presence and heightened security measures have affected life and badly harmed business in the capital.