Officials and witnesses in Cameroon say gunmen dressed in military uniform and carrying signs opposing Cameroon's longtime president opened fire on a major bridge in the commercial city, Douala.

Witnesses say the gunmen blockaded the heavily-traveled Wouri Bridge and exchanged gunfire with security forces for hours early Thursday.

It was not immediately clear how many gunmen were involved. There are reports security forces arrested at least four suspects and that another suspect plunged from the bridge into the river below.

Security officials say the armed men were carrying signs calling President Paul Biya a “dictator” and saying he must leave “at all costs.”

Cameroon is scheduled to hold a presidential election on October 9th.

President Biya has ruled the country since 1982 and 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 and have argued that the old term limits still apply to him.