Police in Edinburgh have accused a "hard core" of determined activists of being "irresponsible" and putting people's safety at risk.
Police and protesters face each other on Princes Street
Anti-G8 protesters fought violent battles with police in the centre of the city, which was brought to a standstill for six hours.
About 90 people were arrested including what police called "key" anarchist suspects from across Europe.
More than 20 protesters and police officers were injured.
The protesters accused police of antagonising the crowd.
At least four police officers were taken to hospital after clashes with demonstrators.
Uneasy stand-offs between police and protesters continued late into the evening.
Lothian and Borders Assistant Chief Constable Tom Halpin said a small group had been determined to cause "as much disruption as possible".
He said: "They are clearly organised and coordinated. We have recovered maps, radios, and mobile telephones.
"Weapons including stones, staves and other light missiles which have been thrown at police officers. There is evidence of weapons being brought into the city, into the city centre by protesters, despite their apparent outward display of good humour."
The demonstration had been billed as the Carnival For Full Enjoyment.
The demonstrators appeared to want to focus on the west end of Edinburgh, which is the city's financial area.
At 1245 BST, the main body of protesters was hemmed in at Canning Street, with no access into side streets.
More protesters tried to join the march at the Shandwick Place end and were pushed back. One managed to climb halfway up a building with a black flag.
There was a report that a group had entered the Caledonian Exchange building, which houses some offices of the financial services company Standard Life. The company said they did not get into their premises.
A further stand-off took place on Princes Street itself, where dozens of police vans containing riot police were stationed.
Police in full riot gear then set up lines, including a 40-strong wall of officers outside the National Galleries of Scotland.
Eyewitness Michael Findlay, 27, said he saw about 30 protesters picking up wheeled supermarket cages and throwing them at two rows of police in full riot gear in Rose Street.
The police line stood firm while behind them about 15 to 20 mounted police looked on.
The Edinburgh resident said bottles were also thrown and the situation appeared volatile.
He said: "The protesters definitely started it, they started throwing things at police."
More than 1,000 police officers were on duty.
Assistant Chief Constable Halpin called police action during the day "robust and proportionate".
He said: "The so-called carnival has been staged without discussion and clearly those involved are determined to cause as much disruption as possible.
"We have always said that we wanted to assist those who wish to make peaceful protest, but in our view it is clear this was never on this group's agenda.
"This is not about protest. This is unacceptable and irresponsible behaviour".
Scottish Justice Minister Cathy Jamieson said that some areas of Edinburgh City centre had faced significant disruption.
Ms Jamieson said: "It is sad and disappointing that a hard core of protesters are more interested in protest for protest's sake and not in joining the rest of the country in focussing on the real issues of poverty and climate change."
Two Green members of the Scottish Parliament who got caught up in the protest criticised the police for antagonising the crowd.
Mark Ballard and Shiona Baird found themselves surrounded on three sides by police in Hanover Street shortly before 1800 BST.
Mr Ballard said: "Police were rushing into the crowd and antagonising them. It was the most surreal and bizarre policing I have ever seen.
"Police seemed to be inflaming the situation by letting innocent bystanders wander into the areas of trouble, then not let them exit."
The MSPs had returned from a mass blockade at the Faslane naval base in Argyll and Bute.
The MoD site is home to the UK's Trident nuclear submarine fleet and has been the focus of protests for many years.
Ms Baird said: "I was astonished that we almost stumbled into this disturbance - and even more shocked to discover that police would not let us leave the volatile areas.
"Faslane today was a textbook peaceful protest and to come across this in Edinburgh was very disappointing."
City taxi driver George Kennedy, 34, of Fairmilehead, said he was terrorised by eight masked men as he dropped an elderly passenger off in Marchmont Road at about 1300 BST.
"They just came out of nowhere and surrounded the cab," he said.
"They were wearing black and had their faces covered. They started shaking the taxi and trying to tip it over, I was angry but also really frightened."
Mr Kennedy said the group were shouting in French or German and shouting English swear words.
He added: "It went on for a few minutes. Luckily about eight police riot vans happened to be coming along the road, they ran off but the police managed to get hold of them."