Italian police made around 40 arrests on Tuesday as protests against the upcoming G8 summit saw demonstrators hurl bottles and set fire to tyres on the streets of Rome, officials and witnesses said.
The flare-up in violence came outside the University of Rome where protestors, some of whom were masked or hooded, chucked bottles and stones towards police vehicles as several dozen riot squad officers gathered.
According to police spokesman, a total of 36 people, including 27 Italians, were arrested in Rome during the course of the morning.
Among the others arrested were four Swedes, two Germans and nationals from Switzerland, France and Poland and a number of weapons, including baseball bats, were seized.
"Everybody has the right to protest, to make their voice heard, provided they do so in accordance with the law," said Gianni Alemanno, the mayor of Rome.
Police also stopped five French nationals, aged between 25 and 35, close to the summit venue in the city of L'Aquila who were found with several clubs.
The group were briefly detained for possessing offensive weapons but were later released.
Around 15,000 police have been mobilised to provide security during the course of the three-day summit which begins on Wednesday in L'Aquila, a city around two hours' drive from Rome.