Nigeria's two main political parties on Saturday hit out at a decision by the country's election watchdog to push back presidential and parliamentary elections by a week.
The Independent National Electoral Commission (INEC) blamed the postponement on logistical difficulties, after reports of widespread problems in the distribution of voting materials.
Yet both the ruling All Progressives Congress and the main opposition Peoples Democratic Party blamed the other for orchestrating the delay as a way of manipulating the vote.
President Muhammadu Buhari's campaign spokesman Festus Keyamo, for the APC, said the news was a "huge disappointment" and hit out at INEC for being unprepared.
Mr Keyamo called on the body to remain impartial "as the rumour mill is agog with the suggestion that this postponement has been orchestrated in collusion with the... PDP".
"We have earlier raised the alarm that the PDP is bent on discrediting this process the moment it realised it cannot make up the numbers to win this election," he added.
"We are only urging INEC not to collude with the PDP on this."
PDP candidate Atiku Abubakar blamed the Buhari government for "instigating the postponement" and said it hoped to disenfranchise the electorate to ensure a low turnout.
"Nigerians must frustrate their plans by coming out in even greater numbers on Saturday 23 February" and for governorship and state assembly elections two weeks later, he added.
With tempers expected to flare, and political violence common in Nigeria, Abubakar called on his supporters to remain calm.
"We will overcome this. You can postpone an election but you cannot postpone destiny," he added in a statement.