At least ten supporters of politician Imran Khan have been wounded after they came under gunfire while en route to an anti-government rally in central Pakistan, police have said.
The incident occurred in Jhelum city in Punjab province on Sunday.
"Ten people were wounded in the firing. One of them is critical and has been taken to hospital in Rawalpindi city," Jhelum's police chief Sarfaraz Wirk told the AFP news agency.
Khan is staging large rallies in major cities calling for the resignation of Prime Minister Nawaz Sharif and the holding of fresh elections.
He has accused Sharif of winning the 2013 elections through widespread voter fraud.
A spokesman for Khan's Tehreek-i-Insaaf (PTI) said security guards of provincial politician Chaudhry Nadeem Khadim - from Sharif's ruling PML-N party - were responsible for the incident.
"I know that their people have been injured but first they [PTI activists] opened fire on my house and then my security guards opened fire in defence," Khadim told local TV channel SAMAA.
Wirk said: "Both sides are blaming each other for the firing but we will investigate the incident."
Khan's PTI party has attracted large crowds in many cities and the former cricketer addressed thousands of supporters at Sunday's rally.
Thousands of PTI activists, along with supporters of populist Muslim leader Tahir-ul-Qadri, began camping in Islamabad in August in protest against the government.
Qadri called off his protest last month and has left for Canada, where he is normally based, but Khan continues to address supporters from the top of a shipping container outside parliament most evenings.
The protests destabilised Sharif's government for a while but have so far failed in their stated aim of bringing down his administration.
Khan has announced a fresh protest rally in Islamabad on November 30.