Harare - Anti-government activists in Zimbabwe vowed on Friday to challenge a police order barring protests in the capital Harare, on the eve of mass demonstrations planned across the country against veteran ruler President Robert Mugabe.A coalition of opposition parties under the banner of the National Electoral Reform Agenda (Nera) is demanding reform ahead of the 2018 vote, including free access to the voters' roll.The month-long protest ban was instituted on Friday, just over a week after an earlier order was overturned by the courts.Nera spokesperson Douglas Mwonzora said the opposition parties would challenge the ban in the high court."This is a typical comedy of errors where the state has fallen into the very same legal trap it fell into last time," he told AFP. "A similar order was challenged before a competent court which declared it invalid and nothing is to be gained by issuing the same order again."Mugabe has vowed a crackdown on dissent and blasted judges for "reckless" rulings allowing previous demonstrations.Promise Mkwananzi, spokesperson for the protest group Tajamuka, said they would march on Saturday, despite the police order."The constitution and the high court allow for peaceful demonstrations," he told AFP. "The police are promoting lawlessness in the country by banning peaceful demonstrations." Mugabe's Zanu-PF party won the last general elections in 2013, which were marred by electoral fraud.Opposition to the ageing leader's 36-year reign has grown in recent months with a surge of public demonstrations, triggered by an economic crisis that has left banks short of cash and the government struggling to pay its workers.Two weeks ago, police detained scores of people including activists and bystanders following violent protests in the capital.Mugabe, 92, has often used brutal force to silence his opponents and warned the protesters last week they were "playing a dangerous game".