By Gift Sukhala

HARARE (Reuters) - Zimbabwean police used teargas, water cannon and batons on Wednesday to disperse opposition youths who demonstrated in the capital against alleged brutality by security agents.

More than 200 youths from the main opposition party, the Movement for Democratic Change (MDC), took to the streets two days before a planned march by all opposition parties to try to force President Robert Mugabe to implement electoral reforms ahead of the 2018 vote.

Police intercepted them and fired teargas at the protesters who were planning to hand in a petition at the offices of the Ministry of Home Affairs, which is in charge of the police.

Two pick-up trucks belonging to state broadcaster ZBC and police were burned, according to a Reuters witness, but it was not clear who had torched the cars or whether anyone was hurt.

Riot police blocked streets around the MDC headquarters and used water cannon against some youths in downtown Harare.

Some protesters threw back teargas canisters, as well as rocks, toward the police, who fired more teargas outside the MDC offices, forcing pedestrians and people standing in nearby bank queues to flee.

The youths had marched through the streets of the capital denouncing the police for beating up protesters and called on Mugabe to step down, accusing him of running a dictatorship.

"We have been seeing a deliberate attempt by the police to intimidate, harass and silence the people of Zimbabwe," MDC Youth Assembly secretary general Lovemore Chinoputsa told Reuters TV during the march.

Chinoputsa said police had refused to sanction the march, saying that it would degenerate into violence.

Police spokeswoman Charity Charamba said she could not comment because she was in a meeting. The police routinely deny charges of brutality and instead accuse the opposition of using "hooligans" during protests to attack officers.

The southern African nation has a history of violence against opponents of Mugabe, where police have in the last few months crushed demonstrations against high unemployment, acute cash shortages and corruption.

A trauma clinic in Harare last month recorded a list of cases of people who had been caught up in a police crackdown during anti-government protests.

The MDC's leader Morgan Tsvangirai and former vice president Joice Mujuru are expected to lead Friday's march.

(Writing by MacDonald Dzirutwe; Editing by James Macharia and Richard Balmforth)