Cameroonian security forces used teargas to disperse about a thousand opposition supporters who had gathered in the commercial capital on Tuesday to protest against President Paul Biya as he marked 30 years in power, witnesses said.Biya, 79, has kept Cameroon, an oil producer and major cocoa grower, on a relatively stable path in a volatile region - although critics say sometimes at the expense of democracy.He won 78 percent of the vote in October 2011 to secure a sixth term, a result that opposition groups denounced as fraudulent.Opposition supporters had gathered at a thoroughfare in Douala to mark the 30th anniversary of Biya’s rise to power when the police and gendarmes charged at the crowd, dispersing them with teargas, said Jean Michel Nintcheu, an opposition member of parliament."We had just started the peaceful march when a large number of well-armed police and gendarmes deployed by the repressive regime of Biya used water cannon, teargas and other weapons to disperse and brutalise thousands of our activists,” Nintcheu said by phone from Douala."What happened to us here in Douala represents what Cameroon has been going through during his 30 years in power,” he said.He said several observers and journalists attending the event were also beaten by security forces.Solomon Amabo Atanga, a journalist with a Douala-based independent media group, estimated the crowd at just over 1,000 people and said it had blocked off traffic to a large part of the city.He said a reporter for another newspaper had been wounded by the police."The police and gendarmes in combat uniform not only brutalised him, they also confiscated my phone and those of four other colleagues and a digital camera from another who was shooting images of the incident,” Atanga said.