Buhari spoke during an emergency meeting of the ruling All Progressives Congress (APC) in the nation’s capital, Abuja, on Monday.
“Anybody who decides to snatch ballot boxes or lead thugs to disturb it [the vote], maybe this is the last lawful action you will take,” Buhari said.
“I am going to warn anybody who thinks he has enough influence in his locality to lead a body of thugs or to disturb the voting system, he will do it at the expense of his own life.”
The president’s speech was condemned by the opposition Peoples Democratic Party (PDP) and civil society organisations.
“The last time we checked, the death penalty wasn’t a sanction in the 2010 Electoral Act. So threatening people with death could be considered an incitement to electoral violence, which is an offence under the act,” PDP spokesman Phrank Shuaibu said.
“Recall this is coming from the same party which said that foreigners who intervene in the election would be sent back in body bags,” Shuaibu added.
The Independent National Electoral Commission (INEC) announced the delay of polls by a week on Saturday following an emergency meeting in Abuja.
The INEC said the postponement was made because of delays in transporting electoral materials.
Buhari also questioned the election delay, calling for an investigation of the role of the electoral body.
“INEC had all the time and all the resources they wanted and then they have to wait for only six hours to casting the votes to tell us that it is not possible. Definitely, the reasons why such incompetence manifest itself has to be explained to the nation,” Buhari said.
“The constitution and the laws protected INEC, but they must not take us for granted,” he added.
The president’s comments further raised concerns about the electoral commission’s independence.
A political science lecturer at the University of Abuja, Abubakar Kari, has called on the INEC to remain “transparent, impartial and neutral”.
“They must be firm but fair and be open and accountable in all they do. This way whatever is the outcome will be credible and acceptable,” Kari told Al Jazeera.