By Nelson Banya

HARARE (Reuters) - A prominent Zimbabwe human rights lawyer and four aides to Prime Minister Morgan Tsvangirai were refused bail on Wednesday in a case that has renewed criticism of President Robert Mugabe's security forces before an election later this year.

Zimbabweans voted overwhelmingly in a March 16 referendum for a new constitution that would curb presidential powers, paving the way for elections later this year. But Tsvangirai and civic rights groups fear Mugabe and his ZANU-PF party is already undermining the chances of a free and fair election.

The day after the referendum, lawyer Beatrice Mtetwa was arrested and accused of shouting at and taking pictures of police officers who were conducting a search at the home of one of Tsvangirai's aides.

Mtetwa, who waved to supporters on Wednesday when she appeared in court in green prison garb, says the charges are fabricated.

Her lawyer described the arrest as an attack on the legal profession a day after the approval of the charter, which reins in the president's powers and expands civil liberties.

Magistrate Marehwanazvo Gofa justified the decision to keep Mtetwa in custody by saying she would "continue to cause commotion and interfere with police investigations".

Marehwanazvo also said Tsvangirai's four aides, who appeared in court in leg irons, were likely to abscond because they faced serious charges of breaching official secrets law, impersonating police and possessing "articles" used to commit crime.

The first offence carries a maximum 20-year jail term.

Pro-democracy groups were furious.

"We as an organization wish to express our outrage at the judgment," the Crisis Coalition, one of several African legal groups to have condemned Mtetwa's arrest, said in a statement.

Lawyers for the five will appeal at the High Court on Thursday. If convicted, Mtetwa, an outspoken 55-year-old lawyer who has represented Tsvangirai in the past, faces a $500 fine or a two-year jail term.

Critics accuse Mugabe of using state security to intimidate and crack down on those opposed to the 89-year-old leader, who has ruled the southern African nation since independence from Britain in 1980. Mugabe denies the allegations.

Mugabe and Tsvangirai agreed to share power four years ago after a violent and disputed election and the uneasy coalition has managed to stabilize an economy wrecked by hyper-inflation.

The two bitter rivals will square off for the third time in a presidential election later this year that will determine if Mugabe, Zimbabwe's only ruler since independence from Britain, will add to his years in power.

(Reporting by Nelson Banya; Editing by Ed Cropley and Mark Heinrich)