Berlin's central Kreuzberg district cleaned up today after the worst May Day rioting by leftist and minority youths in years had injured 273 police and left streets strewn with debris, according to dpa. Police detained 289 offenders during Friday evening's violence, well up from the 139 caught one year ago for overstepping the bounds in an annual May Day ritual that dates back to 1987. Ehrhart Koerting, interior minister of the city-state of Berlin, said it had been much more violent than in previous years. The rioting, which was expected in advance by police and leftists, began when 400 masked militants in a crowd of 5,000 anti-capitalist demonstrators began hurling stones and bottles soon after a parade began. Police dispersed the crowd and tried to catch the offenders. Police deployed tear gas and pepper spray during hours of running battles with an estimated 2,500 rioters, some of them minority youths, who beat up lone policemen, set fire to trash and vehicles and smashed windows. An inflammable liquid was poured over two police officers and set on fire, but the officers were uninjured thanks to colleagues who doused the flames. Medical aid was also hampered when stones were thrown at ambulance crews. A sociologist, Dieter Rucht, rejected suggestions that the fighting represented an upwelling of discontent among the poor amid world recession, saying it was a 22-year-long tradition observed by a militant leftist counterculture numbering about 5,800 Germans. Berlin professor Rucht accused the media of egging on the violence by predicting that the recession could lead to bloodshed. "If no confrontation had developed, the public could have concluded the militants were weak. From their point of view, they had to act," he said. Some 6,000 riot police were deployed during Berlin's second night of violence after clashes had begun Thursday evening, to be followed by brawls with demonstrating neo-Nazis during the daytime Friday. May Day is Europe's labour day, with trade unions and left-of-centre parties holding orderly parades. In recent years, neo-Nazis and the extreme left have used the workers' holiday for their own shows of strength. In the western city of Dortmund, police opened an inquiry against 280 neo-Nazis who attacked a parade of trade unionists with stones and clubs Friday. A police union said neo-Nazis assaulted people and police in five other cities on May Day. On Saturday morning, Berlin sanitation crews cleared up debris and road engineers drew up plans to restore cobbled street surfaces and sidewalk paving ripped up by the rioters as ready ammunition. In another German city, Hamburg, similar street fighting through the night left a car gutted by fire and led to 20 arrests. The leftists at the heart of the violence are linked to anarchist movements in several other European cities and are hostile to the police, who they regard as stooges of capitalism.