A Pakistan politician declared the winner of a provincial assembly seat in last week's election says he will cede to a rival because he believes the result was rigged.

There have been widespread allegations of vote-rigging and result manipulation after authorities switched off the country's mobile phone network on election day and the count took more than 24 hours.

Independent candidates loyal to jailed former prime minister Imran Khan took the most seats in Thursday's National Assembly polls, preventing the army-backed Pakistan Muslim League-Nawaz (PML-N) from securing a ruling majority.

They also did better than expected in simultaneous elections for the country's four provincial assemblies in Khyber Pakhtunkhwa, Balochistan, Sindh and Punjab.

Hafiz Naeemur Rehman, the head of Jamaat-e-Islami (JI) in financial capital Karachi, won his party a seat in the Sindh assembly -- with official results showing he got 26,296 votes, compared to 20,608 for the runner-up.

But Rehman believes the real winner was an independent candidate linked to Khan's Pakistan Tehreek-e-Insaf (PTI) party, who was listed as fourth with 11,357 votes.

"As a conscientious man, I declare that the PTI-backed candidate has won and I will not avail that seat" Rehman told a press conference Monday.

"I will not accept any extra votes granted to me."

PTI lauded the move on social media.

"This will give strength to many others who were forced by regime to take fake mandate," the party said on X, formerly Twitter.

Dozens of petitions have already been filed by losing candidates claiming they were robbed of victory by vote-rigging or manipulation of the count.

Rehman, however, is the only case of a winner alleging that rigging gave him victory.

The Islamist party is also challenging results that went against them in several other constituencies.

"We have four petitions pending in the high court and compiling rigging evidence on more seats to be filed in the court," party spokesman Zahid Askari told AFP.

With no clear winner of the national vote last week, Pakistan has weeks of political uncertainty ahead.

Dozens of constituency results are facing challenges in court and rival parties negotiating possible coalitions.