Zimbabwean opposition leader Morgan Tsvangirai says the beating he received at the hands of police should be an "inspiration" for the struggle.
Mr Tsvangirai was speaking from hospital as he received blood transfusions for internal bleeding and treatment for a fractured skull.
He and 49 opposition activists were arrested at a rally on Sunday.
Zimbabwe's information minister said the injuries had been inflicted when Mr Tsvangirai and others attacked police.
Sikhanyiso Ndlovu told the BBC that police confiscated "killer" weapons from the activists, adding that four policemen were in hospital as a result of the attacks.
The government said the rally breached a ban on political gatherings imposed after violence at a demonstration last month.
UK Prime Minister Tony Blair described the situation as a tragedy for the people of Zimbabwe.
The action against Sunday's demonstration was also strongly condemned by the UN Secretary General, Ban Ki-moon, the United States and European Union.
US State Department spokesman Tom Casey said extra sanctions were being considered against Zimbabwe following the arrests. The UK has urged European governments to bring in similar measures.
Current sanctions include a travel ban and asset freeze for senior officials.
South Africa also criticised its neighbour, urging Mr Mugabe to respect the rights of citizens, including opposition leaders.
BBC Africa editor Martin Plaut says that after years of fending off international pressure, Pretoria has adopted an entirely new tone.
The activists appeared in court - many bandaged and bruised - but were all then released from police custody after prosecution lawyers apparently failed to appear.
A number remained in hospital on Wednesday.
Mr Tsvangirai, who heads the Movement for Democratic Change (MDC), said violence he and others endured at a police station was intended to inflict as much harm as possible.
He said he suffered head injuries, for which he received six stitches, and took "body blows" to the arms, knees and back, and that he lost two pints (one litre) of blood.
Correspondents say there were an astonishing number of broken arms among the activists' injuries, indicating a very high level of physical violence.
"There are lots of people who've been subjected to this kind of torture, this kind of brutality by this regime," Mr Tsvangirai said in an interview from his hospital bed.
Mr Tsvangirai has been the figurehead for the movement opposing President Robert Mugabe.
"It just shows the extent to which this desperate regime is trying to protect its power," he said.
"For the struggle, I think it's an inspiration to everyone. There is no freedom without struggle, and there is no freedom without sacrifice."
A witness told the BBC the activists turned on police after one of their number was shot dead, but Mr Tsvangirai denied attacking the police.
"If there were any skirmishes, it was nothing to do with me," he said.
Civil discontent in Zimbabwe is rising over the country's economic crisis, with chronic unemployment and inflation running at more than 1,700% - the highest in the world.