A riot triggered by the suspension of a train service has left more than 20 people injured in an Argentine suburb.
More than 80 people were arrested during the five-hour rioting
Passengers and masked demonstrators set fire to their train after being told it would not leave Haedo station, about 15km (nine miles) west of Buenos Aires.
Six police officers were among those injured during the five-hour rioting. More than 80 people were arrested.
The clashes come as the country prepares for the Americas summit, to be attended by George Bush among others.
The Argentine authorities said they believed the incident had been instigated by members of the railway unions and leftist groups.
Violence broke out after officials of private rail company TBA announced to the nearly 2,000 travellers on board the train that it would not leave the station due to technical problems.
The passengers had already been held at Haedo station for about 50 minutes.
Witnesses said that the passengers got off the train and, joined by dozens of people wearing masks, began to hurl rocks at the train, breaking windows.
The masked demonstrators also set fire to several train carriages and a police vehicle. Nearby stores were destroyed by the flames.
Police officers used rubber bullets to contain the violence.
"This was planned, these were armed groups," said Interior Minister Anibal Fernandez.
Correspondents say the incident was one of the worst in the country since the street rioting seen during Argentina's economic collapse four years ago.