Three opposition parties call for cancellation of the election, as the ruling party candidate is in the lead, with results from 19 of 36 states announced.

Provisional results announced by the Independent National Electoral Commission (INEC) from 19 of Nigeria’s 36 states put the APC’s presidential candidate Bola Tinubu in the lead, ahead of Atiku Abubakar of the People’s Democratic Party (PDP), Peter Obi the Labour Party (LP) and Rabiu Kwankwaso of the New Nigeria People’s Party (NNPP).

On Wednesday, the LP, PDP and the African Democratic Congress called for new polls during a joint news conference held in the capital, Abuja, saying the wait for the announcement of the final result would be “like waiting to treat a dead body”.

“We monitored with dismay the travesty to democracy exhibited at the collation centre of INEC. It is, to say the least, a rape on democracy,” said Julius Abure, the LP chairman, alleging widespread manipulation.

“We are therefore constrained to state that INEC compromised the integrity of the election even before collation began … We have therefore arrived at the conclusion that the election has been irretrievably compromised.”

The parties also called for INEC Chairman Mahmood Yakubu to step down from his position and be replaced by “a credible person from outside the commission”.

“Election results are still being manipulated in government houses,” Abure alleged. “If you send your child to school and it fails exams, they repeat the class. INEC has failed,” he said. “The results announced by INEC so far show monumental disparities between actual results reported by our party agents and indeed millions of Nigerians on election day.”

“What we have seen is vote allocation and not collation,” added Dino Melaye, a PDP politician and former senator who moderated the news conference.

Since Saturday’s election, observers, voters and civil society leaders have complained about logistical challenges in the conduct of the polls and the slow pace of uploading result sheets from polling units to a new electronic portal designed to improve electoral transparency.

That has allowed room for the manipulation of results, the critics say, without providing any specific names so far.

“Collation in Nigeria is a black hole – nothing that comes out is to be trusted without a means of verification,” Ayisha Osori, former executive director of the Open Society Initiative for West Africa, told Al Jazeera. “As a low-trust society, we welcomed IReV [the results viewing portal] as a means of verifying our polling unit results. Without this transparency, results written by a few men become difficult to accept.”

The APC has dismissed the opposition’s allegations, urging the INEC to announce the result quickly to defuse the situation.

Meanwhile, former President Olusegun Obasanjo on Monday wrote an open letter addressed to outgoing President Muhammadu Buhari, claiming that INEC officials had been compromised and the results doctored.

He urged Buhari to “let all elections that do not pass the credibility and transparency test be cancelled”.

“Let me appeal to the Chairman of INEC, if his hands are clean, to save Nigeria from the looming danger and disaster which is just waiting to happen,” Obasanjo added.

The opposition also spoke of the need for the president to cancel the disputed elections, even as the nation waits for results to be announced and there are mounting concerns that there could be post-electoral violence.

“We don’t want Nigerians to take law into their hands, and we representatives have the responsibility to take this action,” said former Nigerian Senate President Iyorchia Ayu, the PDP’s chairman.