Authorities and eyewitnesses in Cameroon say several gunmen dressed in military uniforms have opened fire on a major bridge in the country's largest city, Douala.

The gunmen reportedly blockaded the bridge, exchanging fire with security forces. There have been no reports of injuries, and at least four of the gunmen have been arrested.

A security official says one of the men was holding a banner urging President Paul Biya to step down.

The incident comes just 10 days before Cameroon holds presidential elections.

President Biya, who has ruled the country since 1982, is widely expected to win another seven year term.

In 2008, the 78-year-old Mr. Biya pushed through constitutional changes that eliminated term limits.

The changes triggered anti-government riots in which at least 40 people were killed.

Some opposition supporters have urged Mr. Biya to step down, or they argue that the old term limits still apply to him.

The election will be held October 9. Official campaigning began on September 15.