Police also reported extensive property damage, including the burning of several gas stations and homes and the campaign office of President Goodluck Jonathan. The clash is the latest incident in increasing election-related violence countrywide.
The ruling party is not to blame for the violence, according to Paschal Bafyau, a member of the Contact and Strategy Committee of the Goodluck Jonathan campaign organization.
He says the opposition, unable to present better ideas than President Jonathan, is resorting to violence.
"Usually, people who do not have hope of winning elections are in the habit of disrupting anything constructive that would lead to peaceful elections," he says. "So they are these pockets of disgruntled elements that try to disrupt campaigns, but there will be peaceful elections in Nigeria."
Bafyau disagreed with critics who say the ruling party's grip on power in most states leaves the opposition little room to campaign, causing them to lash out in violence.
"It is not true because usually most of the disruptions are aimed at the ruling party. It is not the ruling party that is disrupting rallies of other parties. It is other parties that are disrupting the rallies of the ruling party. So we are in no way involved in the disruptions at all."
The opposition Action Congress disagrees. Officials say youth supporters of the PDP routinely invade opposition campaign to attack candidates. Police authorities say most of the attacks are carried out by well-armed youths.
Bafyau appealed to them to refuse to be recruited by what he called desperate politicians.
"It is very unfortunate. Programs are on in our televisions to discourage youths that are being used as thugs because people who are using the youths do not use their own children. Their children are usually safe at home," he said.