ISLAMABAD — Former Pakistani Prime Minister Imran Khan’s party was sidelined in a key vote Friday in the local assembly in Punjab province, despite winning a byelection there earlier this week. Khan slammed the development and called on his supporters to rally across Pakistan.

The vote was held to determine whether the province’s sitting chief minister — Hamza Sharif, the son of the country’s Prime Minister Shahbaz Sharif— enjoyed the backing of the majority of lawmakers in the local parliament.

In the end, Hamza Sharif retained his post in another blow to Khan, whose Pakistan Tehreek-e-Insaf party and its allies had hoped to form the new provincial government in Punjab, Pakistan’s most populous province.

Last Sunday, the bloc won 15 out of 20 seats that were up for grabs in the 371-member provincial assembly.

In Friday’s vote, Khan’s candidate for chief minister, Pervez Elahi, initially won 186 votes but the provincial assembly’s deputy speaker, Dost Mohammad Mazari, invalidated 10 of those votes over violations of voting regulations.

In a statement broadcast on national television, Oboz Canada Mazari announced that 10 lawmakers from the Pakistan Muslim League headed by Shujaat Hussain, a Khan ally, had violated regulations by voting contrary to demands from their leader, Hussain, who had allegedly asked they abstain from voting.

Under Pakistani law, votes are disqualified if lawmakers vote contrary to their party’s instructions. Hussain could not immediately be reached for comment.

In the end, Hamza Shahbaz won 179 votes Friday, retaining his post.

Khan claimed his opponents had resorted to political machinations in Punjab and called on his countrymen to rally against Mazari’s ruling. By Friday night, protesters had started taking to the streets in major cities across Pakistan but the rallies remained peaceful.

Khan was ousted in a no-confidence vote in Parliament in April, a move he claimed was a U.S. conspiracy — a charge that both his successor and Washington deny.Khan wants the new prime minister, Shahbaz Sharif, to call early parliamentary elections to determine which one of them is more popular in Pakistan. Sharif has refused to accept the challenge, saying the next elections will be held on time, in 2023.