Armoured police vehicles began speeding through chanting crowds
Nigerian soldiers have confronted opposition supporters demonstrating about an election result in south-western Ekiti state.
They fired shots and tear gas to disperse demonstrators outside the Action Congress (AC) headquarters in the state capital, Ado Ekiti.
The town is now quiet after politicians called for calm following a face-off.
Nigeria's governing People's Democratic Party (PDP) narrowly won the disputed re-run election.
The BBC's Caroline Duffield in Ado Ekiti says residents hid indoors, covering their windows as hundreds of soldiers sealed off the area around the headquarters.
Armoured police vehicles with mounted machine guns began speeding through chanting crowds, at one point driving up to the AC headquarters and pointing guns at the building and gesturing at the people watching inside it.
Protesters and shopkeepers ran for cover as shots were fired over the crowds and clouds of tear gas spread through the neighbourhood.
The results of the election for the post of governor held last week were delayed by claims of violence and intimidation.
Voting in one area was delayed until Tuesday.
Furious opposition leaders cried foul and vowed to challenge the result in a state they regard as a stronghold.
The original poll two years ago was won by the candidate of the governing PDP.
But Segun Oni was thrown out of office and the result overturned as it became mired in allegations of mass vote fraud.
Our correspondent says the latest outcome means Mr Oni will now return to office.
Heavily armed police and soldiers were out in force in the town of Oye Ekiti, where Tuesday's vote took place.
Our correspondent says opposition supporters were enraged as the electoral commissioner declared victory for the PDP by a slender margin of 4,000 votes.
Several dozen men in the crowded hall shouted the commissioner down.
Opposition AC governorship candidate Kayode Fayemi said later the result was a "travesty" and his party would challenge it in court.
"Our ballot boxes were snatched in daylight, our monitors were beaten up," he told the BBC's Network Africa programme.
Our correspondent says both parties have traded accusations of hiring thugs to intimidate people, bribing election officials and rigging votes.
The electoral commissioner was supposed to announce poll results last week after the initial re-run but refused to do so, alleging fraud, and temporarily went into hiding.
Her actions sparked angry demonstrations, involving women marching half-naked in the streets in anger.
The poll was seen as strategically important for both parties.
Our correspondent says the PDP had hoped to prevent the AC winning a stronghold that could unite with the east of the country to challenge the governing party.
Nigerian President Umaru Yar'Adua has said the situation in Ekiti underlines the need for urgent reform of Nigeria's election system, with the country's next general elections looming in 2011.