Nigerian President Goodluck Jonathan vowed on Thursday that the country's final round of elections would go ahead next week despite rioting which has killed at least 100 people across the mostly-Muslim north.

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".