Rioting hit parts of Nigeria's north overnight as President Goodluck Jonathan headed for a first-round victory in the country's elections, police and residents said on Monday.
Allegations of vote rigging led to street riots in parts of the states of Kaduna and Sokoto. Earlier, buildings had been burnt in Bauchi and Gombe states.
There were reports of at least two people killed, but police did not confirm any casualties.
"Security men have been deployed to the city (of Sokoto) to contain the restive youths who are on the streets burning bonfires in protest," said Sokoto police spokesman Al-Mustapha Sani.
In Kaduna, residents said the homes of ruling party figures had been attacked and gunshots were heard. Police said extra personnel had been deployed, but had not confirmed details.
An explosion rocked a hotel in Kaduna on Saturday night as voting wrapped up, wounding eight people, according to police.
Jonathan was on course to win the country's elections as official results showed him with a huge lead, but concerns have been raised over regional divisions.
The president was strong in his native south, while his main challenger, ex-military ruler Muhammadu Buhari, had support across much of the north.
Nigeria's 150 million population is roughly split between a mainly Muslim north and predominately Christian south.