About 15,000 opposition activists gathered on Saturday in Azerbaijan's capital, Baku, to protest the outcome of the 6 November parliamentary elections, which they said were rigged - the latest in a series of such opposition actions in recent weeks.
Unlike previous rallies, the demonstrators on Saturday tried to set up a permanent protest on a square in downtown Baku, triggering a swift police crackdown - the first time since the vote.
After opposition leaders said they were going to stage a sit-in on the square, police, in riot gear, rushed to disperse them, beating them with truncheons and pushing them away.
Protesters shouted "Freedom!" and some hurled stones at the police who hid behind shields.
Hundreds of soldiers and police officers quickly pushed protesters away from the square. They shattered a stand used by opposition leaders and broke the opposition's orange banners - the colour borrowed from Ukraine's Orange Revolution.
Baku's deputy police chief, Yashar Aliev, said 18 officers were injured in the clash with the protesters. He added that 29 rally participants had been detained.
Riot police used truncheons,
water cannons and tear gas
Police used water cannons to drive protesters away from a nearby street.
Opposition leaders said scores of protesters were beaten and many were badly injured, some admitted to hospital.
"They used force against a peaceful rally without any prior notice," said Ali Kerimli, head of the Popular Front, one of the parties in the Azadliq (Freedom) opposition bloc that organised the protest.
"Today Azerbaijani authorities showed their real face."
Police officials, at a news conference, justified the use of force against the demonstrators, saying the demonstration "was not peaceful". They branded the opposition as "provocateurs".
They said the authorities had allowed the rally to last for two hours, and police intervened only after the deadline expired and the protesters' leaders said they were turning it into a sit-down rally.
The US denounced the police action.
"We deplore the unjustified and unprovoked use of force against citizens peacefully exercising their right to freedom of assembly," the US embassy in Baku said.
"The US embassy strongly condemns the police violence today against supporters of the Azadliq bloc," it said, and called on the government to "punish those responsible".
"They used force against a peaceful rally without any prior notice. Today Azerbaijani authorities showed their real face"
Ali Kerimli, head of the opposition Popular Front party
International observers had criticised the 6 November polls, saying they fell below democratic standards.
But Western countries concerned about maintaining stability in the oil-rich Caspian Sea state bordering Iran have not endorsed opposition demands for repeating elections.
The elections gave President Ilham Aliev's government victory but trimmed his party's dominance of the 125-seat national legislature to just under the absolute 63-seat majority it won under preliminary vote results.
The opposition won only 10 seats, while the rest went to little-known independent candidates, generally regarded as ready-made allies of the ruling party.
Regular opposition protests had encouraged expectations that Azerbaijan was heading for a popular uprising like those that brought opposition leaders to power in other former Soviet nations of Georgia, Ukraine and Kyrgyzstan.
But the opposition has failed to capitalise on resentment over corruption that has helped to keep more than 40% of people in poverty despite the country's oil wealth.
Official restrictions on demonstrations along with widespread public apathy and the opposition's weakness mean that attendance at rallies often falls short of expectations.
Kerimli said the opposition would stage another rally next Saturday.