By Tom Esslemont
BBC News, Tbilisi
So far, only one piece of CCTV footage of an attack has been released
Human Rights Watch says it has documented dozens of cases of attacks against opposition activists by unidentified assailants during anti-government demonstrations in the Georgian capital, Tbilisi.
In a letter to the Georgian interior minister and justice minister, the director of the organisation's Europe and Central Asia division, Holly Cartner, says the attacks follow a striking pattern.
She says that usually the victims have been assaulted while leaving the sites of the near-daily rallies, which began last month.
The protesters have been calling on President Mikhail Saakashvili to resign, citing disappointment in his ability to strengthen the rule of law and to improve democratic freedoms.
HRW says it fears the attacks "appear to be a concerted effort to intimidate the demonstrators" and to prevent them "from exercising their right to freedom of assembly".
The government says it has launched an investigation into each of the attacks, some of which resulted in broken bones and concussion.
But one government official has told the BBC that he thinks the opposition is also responsible for provoking other undocumented attacks and for causing a split in Georgian society.
'Men in masks'
Natia Archvadze, a student, told HRW how on 9 April, the first day of demonstrations, she and three friends were driving across a bridge in the centre of Tbilisi when two unlicensed 4x4 vehicles pulled up alongside.
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"They blocked our way from the back and the side. About 15 men in masks came out and... started beating us," she was quoted as saying.
I met one of Ms Archvadze's friends, Lasha Kopaliani, 20, also a student and the principle victim of the attack she described.
On Baratashvili Bridge, he showed me the exact spot where he says he was beaten by a group of masked men.
"They started hitting us with rubber truncheons. They hit me across the chest and from the back until I fell," he said.
Mr Kopaliani told me that he was surprised that traffic police who had moments earlier stopped him and his friends to check their papers, had not reacted when the unmarked vehicles pulled up.
According to Giorgi Gogia, a Tbilisi-based researcher for HRW, many of the attacks have followed a pattern.
"There was a striking pattern in the timing that the attacks took place, the vehicles that the attackers were driving, the appearance of the assailants, the masks they were wearing, and the truncheons they were carrying," he said.
Mr Gogia said HRW had sent the letter to the government to try to ensure that the investigation would be more thorough and conclusive than those carried out here in the past.
Apart from personal testimonies, there is little evidence to back up the allegations and, so far, only one piece of CCTV footage has been released.
The picture is unclear, but it is possible to see five cars stopping abruptly in a dimly-lit back street at night.
Men dressed in plain clothes get out and drag a man out of a sixth vehicle before beating him and leaving him lying on the ground.
The event is watched by nearby security guards at the Tbilisi branch of the World Bank.
Government officials point out that the attacks documented by Human Rights Watch took place between 9 and 25 April.
Ako Minashvili, chairman of the Georgian parliament's committee on foreign relations, says the number of attacks had diminished since police started patrolling the areas where the demonstrations were taking place.
"Maybe [the government] made a mistake at the initial stage by deciding not to have a police presence around the manifestations," he says.
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The government decided against putting large numbers of police on the streets to avoid possible provocations by protesters and clashes, such as those which occurred in November 2007.
But the leaders of Georgia's opposition parties, who organised the protests, have been coming under fire for being too radical.
"We should look deeper into the cases to understand the trends," Mr Minashvili says.
"In the early stages of the demonstrations there were a number of clashes between opposition protesters and citizens which were mainly initiated by opposition leaders who were very radical in their wording and at times very insulting and it caused a split in society," he adds.
One thing is clear - there is a sense of a growing divide in Tbilisi between those who want the rallies to continue and those who yearn for them to end.
The city's main street is still blocked with mock prison cells, a symbol the opposition protesters are using to demonstrate their frustration with what they call President Saakashvili's failure to improve democratic freedoms in the country.
But now there are also many in the city who would be happy to see the blockade removed even if that meant ending the protests without achieving the political change they once craved.