Nigerian youths have been rioting in the south-western Ekiti state after the murder of a leading local politician.
Nigeria's police chief has gone to the state capital Ado Ekiti to take personal charge of the investigation into Ayodeji Daramola's killing.
He was found stabbed on Monday after addressing a rally the day before.
Mr Daramola was a leading ruling party aspirant for governorship elections due next year and is the third high-profile figure to be murdered this year.
Three weeks ago, another leading People's Democratic Party (PDP) candidate for governor in neighbouring Lagos state, Funsho Williams, was also murdered.
So far, nobody has been charged with the killing.
The BBC's Sola Odunfa in Lagos says there's growing concern there could be a spate of assassinations in the run-up to the national elections.
Police Inspector General Sunday Ehindero has travelled to Ado Ekiti, some 300km from Lagos, to take charge of the case.
According to reports from Ado Ekiti, Mr Daramola was stabbed to death last night less than 12 hours after addressing a mass rally.
The killing took place in his country home in Ijan Ekiti which is only a few minutes drive from the state capital.
As news of the murder spread violence broke out in the state.
On Monday evening, young men took to the streets burning houses and cars in Ado Ekiti.
Ekiti's state government has offered a reward to anyone with information that will lead to the arrest of the killers.
Our correspondent says the states most vulnerable to pre-election violence are those where the incumbent governors are seeking re-election.
In these states the governors are intolerant of any opposition from either within or outside their parties, he says.
In others, like Lagos, the violence so far has been among candidates of the same parties in a battle for nomination at the primaries.