Shahbaz Sharif, brother of jailed former prime minister Nawaz Sharif, said on Twitter
there had been “massive rigging” in Khan’s favor amid widespread allegations of military interference in the general elections.
“We will use all political and legal options for (redress) of these glaring excesses,” he added.
The leader of the Pakistan People’s Party (PPP), Bilawal Bhutto Zardari, son of the late leader Benazir Bhutto, also took to Twitter to say he would reject the results over concerns of ballot rigging, saying it was “inexcusable (and) outrageous.”
Khan looked set to become Prime Minister as projected partial results suggested his center-right Pakistan Tehreek-e-Insaf, or PTI, had exceeded expectations.
Partial results showed Khan’s party is set to secure 106 seats in the 342 seat National Assembly, the state-run PTV reported. Sharif’s PMLN (Pakistan Muslim League) is set to win 63 seats, PTV said, while the PPP will take 46 seats.
PTV’s estimations are based on unofficial preliminary results released by Pakistan’s Electoral Commission (ECP).
“The results, as they stand, are striking to say the least,” said Michael Kugelman, a South Asia expert at the US-based Wilson Center.
“While a PTI victory was definitely a strong possibility, a victory by such a wide margin was unexpected and gives the PML-N and other losing parties more reason to allege electoral foul play.”
Khan is due to address the nation on Thursday at 2 p.m. local time, his spokesman Naeem ul Haq said, “in celebration and recognition of the massive support received from the people of Pakistan.”
Khan’s supporters were already celebrating in the streets of Lahore and Islamabad, dancing and waving flags bearing his image.
Security was ramped up outside Khan’s residence in the capital, said Najeeb Ur Rehman Bugvi, senior superintendent of police.