Islamabad, Pakistan - In a rare show of unity, major opposition groups in Pakistan have brought thousands of people into the streets of Lahore in a massive rally to increase pressure on the country's government.

Wednesday's demonstration in the eastern city, considered the political heartland of the ruling PML-N party, was called by Tahir-ul-Qadri, a religious scholar and founder of the Pakistan Awami Tehreek (PAT).

Senior figures from the PPP and PTI opposition parties, the two major political forces rivalling the PML-N, also joined, as did politicians representing other groups.

Qadri called the protest with the explicit demand for Shahbaz Sharif, chief minister of Punjab province, to resign, following the release of an inquiry report that implicates his government in the killings of 14 of the scholar's political workers less than four years ago.

Sharif is the younger brother of Nawaz Sharif, who leads the PML-N party and was removed as prime minister in late July by Pakistan's Supreme Court, over corruption allegations. The Sharifs' party has remained under considerable pressure since then, with several family members facing corruption cases.

Qadri's political workers were shot dead outside his political headquarters in Lahore, after police opened fire on them for resisting a bid to dismantle barriers erected outside the building.

In December, the commission's report was made public after the Lahore High Court ordered authorities to release it.

The inquiry, carried out by a sitting high court judge, held that the authorities had acted with disproportionate force in a manner that was planned, and that officials deliberately withheld information on who had ordered them to fire.

Fractured unity

At the protest on Wednesday, Qadri was joined by, among others, PPP co-chairman and former Pakistani President Asif Ali Zardari, as well as opposition PTI chief Imran Khan.

"This show of political strength is an illustration not of my power, but of the power of the martyrs of Model Town," said Qadri, addressing the crowd.

"All of the country's political and religious parties' leadership is here ... to help the oppressed."

The show of unity was somewhat marred, however, by the refusal of Zardari and Khan to share the stage with one another. As a result, Zardari addressed the crowd and left shortly afterwards, with Khan then arriving at the site of the protest.

Zardari's exit saw many PPP supporters leave the protest. Supporters of Qadri's PAT, Khan's PTI and the PML-Q, Sunni Tehreek and other parties remained, however.

The differences between PPP and PTI suggest there will be no grand alliance between the opposition parties to topple the government.

The PML-N, elected in 2013, insists it will complete its term in mid-2018 and hold a general election on time.

"In 2018, only those who the people vote in will come into power," Marriyum Aurangzeb, the country's information minister, had told reporters in the capital, Islamabad, earlier on Wednesday.

Qadri and Khan have led calls for the government to resign in the past. In 2014, they staged a joint sit-in outside parliament that lasted four months and brought the government quarter of Islamabad to a standstill.

Asad Hashim is Al Jazeera's Web Correspondent in Pakistan. He tweets @AsadHashim