Angry youths launched violent protests in northern cities this week after Jonathan, a Christian from the south, was declared the victor of a weekend election, defeating former military ruler and northern Muslim Muhammadu Buhari.
Churches, mosques and homes were set ablaze in the worst unrest for years as Buhari supporters rejected the outcome.
“These acts of mayhem are sad reminders of the events which plunged our country into 30 months of an unfortunate civil war,” Jonathan said, referring to killings which led to a conflict in which one million people were killed in the 1960s.
In the worst of the violence on Monday, hundreds suffered gunshot and machete wounds, some of them children, and thousands were displaced. The unrest has since been largely brought under control by curfews and a heavy military presence, but two people were killed and a mosque burned in Kano on Wednesday.
“These disturbances are more than mere political protests. Clearly, they aim to frustrate the remaining elections. This is not acceptable,” Jonathan said. “Enough is enough.”
He said he had authorised the security forces to use “justifiable force” to stop the violence and vowed that those responsible would be brought to justice.
Some of the rioters in the northern cities of Kano and Kaduna chanted Buhari’s name as they went on the rampage. Buhari has distanced himself from the violence and called it a spontaneous outpouring of anger against the ruling party.
The government says it was “unprovoked and premeditated”.
The rioting has raised questions over whether Africa’s most populous nation will be able to hold governorship and state assembly polls in its 36 states on April 26, the third and final stage of its election cycle after last Saturday’s presidential race and parliamentary polls the previous week.
Jonathan was steadfast.
“I assure you all that calm is being restored in troubled parts of the country and that the elections scheduled for next Tuesday will go on as planned,” he said.
State governors are powerful figures in the African oil producer, controlling budgets larger than those of some African countries and wielding influence over policy.
The elections had already been expected to be the most volatile of the three polls but the violence this week has raised the stakes even further.
Homes of ruling party members, electoral commission offices and police stations have been targeted, as have members of the National Youth Corps, who are helping run the elections.
Buhari, who said on Wednesday the rigging of results had been enough to deprive him of victory, has failed to issue a clear call to youths perpetrating violence in his name to stop.
He told foreign journalists at his residence in Abuja on Wednesday that he would be out campaigning later this week for his Congress for Progressive Change party ahead of next Tuesday’s state governorship votes.