ISLAMABAD, Pakistan — Tens of thousands of opposition supporters, led by a former cricket star, Imran Khan, and a cleric, Muhammad Tahir-ul Qadri, converged on the Pakistani capital late Friday for what they billed as an extended protest movement to oust Prime Minister Nawaz Sharif.

The two cavalcades, which were loosely allied but operated separately, arrived in Islamabad in the pouring rain, at the end of a slow and occasionally violent journey across Punjab Province.

Mr. Khan’s supporters clashed with pro-government activists as they passed through the city of Gujranwala; each side threw stones and accused the other of starting the trouble. But the peaceful arrival of the protesters in Islamabad was a relief after weeks of political tension and speculation that new turmoil could tempt the military to intervene.

The protests are the most potent threat yet to Mr. Sharif’s 14-month-old government, which has also been dogged by tensions with the military high command. Mr. Khan hopes that, by bringing a large crowd into central Islamabad, he can force Mr. Sharif, whom he accuses of vote rigging, to resign and hold new elections.