The strike was marred by violent incidents
Opposition groups in Zimbabwe say that government security forces have arrested and beaten hundreds of people following last week's widely observed general strike.
Amnesty International says that up to 500 people have been detained in "a new and dangerous phase of repression".
Following the strike, President Robert Mugabe warned the opposition Movement for Democratic Change not to instigate violence, saying: "Those who play with fire will not only be burnt but consumed."
The BBC's Barnaby Philips in Johannesburg says that all the evidence points to a new crackdown of unprecedented brutality.
A doctor working in a hospital in the capital, Harare, said more than 250 people have been treated there after being beaten by the security forces; many had broken fingers or toes, some had broken legs.
Two women described how men in military uniforms stripped them, beat them, and used guns to sexually abuse them.
The MDC says that children of opposition activists have been assaulted.
Lawyer and director of the publishers of the Daily News Gugulethu Moyo says she was beaten by five men in Harare central police station after going there to enquire about a Daily News photographer who had been arrested.
"The cells were so full I had to stand, which was okay because my backside was so bruised I could not lie down," she said.
"We are fast losing count of people being detained and tortured because it's now happening every hour," MDC spokesman Paul Themba Nyathi told Reuters news agency.
Zimbabwean police spokesmen Bothwell Mugariri said about 400 opposition members have been arrested since last week's strike.
This woman, 60, says she was beaten by soldiers
He said many had been charged with malicious injury to property.
The police have denied the torture allegations.
"The police would want to interview and charge everyone who was involved in any kind of violence and we are not going to get distracted by people who organise violence and then cry foul when the law is applied to them," a spokesman said.
During the strike, stones were thrown at passing cars and a bus was set on fire.
The police also say that the offices of the ruling Zanu-PF party were set on fire in Chinhoyi, north of Harare, while explosives were found in the central town of Kadoma.
Zimbabwean human rights activist Tony Reeler says the attacks are focused on the MDC's local leadership.
Following the strike, the MDC gave Mr Mugabe until 31 March to agree to 15 demands including ending torture and depoliticising the police force or face further "popular mass action".
Tension is rising in Harare ahead of two by-elections this weekend in seats the MDC won easily in June 2000 elections.
Zimbabwe, once a regional breadbasket, now has massive unemployment, long fuel and bread queues and inflation of more than 200%.
Up to half the population, some seven million people, need food aid according to donors.