Lagos - Police threw a security cordon around southwestern Ekiti state, restricting movement and deploying riot squads to curb election-linked violence.
A vote takes place on Saturday to elect a new governor, with incumbent John Kayode Fayemi, of the main opposition All Progressives Congress (APC), looking for re-election.
The state has a history of election violence and last week, a party supporter was killed after an APC political rally in the state while dozens of others were injured.
Nigeria's police chief Mohammed Abubakar has placed "an order banning movements in and out of Ekiti State with effect from 6:00 pm (1700 GMT) today (Thursday)," the force said in a statement.
All entry and exit points in four neighbouring states will also have an increased police presence, it added.
The ban on movements "is informed by the need to forestall plans by criminal elements to undermine the electoral process as gathered through intelligence reports," it said.
Politicians and their supporters have been warned against making statements that could incite violence.
"Offenders will not be spared," Abubakar warned in Ado-Ekiti, the state capital.
Local television stations showed footage of riot police, armoured police personnel carriers and sniffer dogs. Residents said heavily armed soldiers were guarding state borders.
Fayemi is expected to be challenged by former governor Ayo Fayose, who is the candidate of the Peoples Democratic Party (PDP) of President Goodluck Jonathan.
The PDP is keen to win back Ekiti after suffering a recent loss of support nationwide.
In 1983, scores of people were killed and hundreds of houses were destroyed when riots broke following the outcome of a disputed gubernatorial election in the old Ondo state, from which Ekiti was created.
International observers, including from the United States and Britain, will be monitoring Saturday's vote, which comes before Nigeria goes to the polls to elect a new president next February.
"A well-conducted election in Ekiti that is free of violence and that accurately reflects the will of the voters would both constitute an important demonstration of the credibility of the electoral system as the February 2015 elections draw closer, as well as bestow legitimacy on the winner of the election," the United States said in a statement.