Clashes broke out yesterday as tens of thousands of Pakistani protesters from two anti-government movements slowly converged on the capital, presenting the 15-month-old civilian government with its biggest challenge yet.

The unrest has raised questions over stability at a time when the nuclear-armed nation of 180 million is waging an offensive against Pakistani Taliban militants and the influence of anti-Western and sectarian groups is growing.

A stone-throwing mob brandishing ruling-party posters attacked the convoy of former cricket star and opposition politician Imran Khan as he led supporters through the eastern city of Gujranwala. Khan’s convoy was shot at but he was not injured, his spokeswoman said. The government insisted shots were not fired and promised an investigation.

“The Chief Minister of Punjab has ordered an inquiry and all those responsible for scuffles will be held accountable,” the statement said. “There were absolutely no gunshots fired at his rally and such PTI-driven sensationalism is unfortunate.”

Khan’s Pakistan Tehreek-e-Insaaf party and supporters of populist cleric Tahir ul-Qadri are slowly heading towards Islamabad, where they plan to occupy main streets until Prime Minister Nawaz Sharif resigns.

In the capital, authorities blocked main roads with shipping containers and barbed wire in an effort to control the marches.