Clashes broke out between protesters and police near the United Nations (UN) building in Geneva on Sunday, on the eve of the G7 summit in the nearby French resort town of Evian.
The protesters threw bottles, stones and firecrackers at the police, which responded with tear gas and water cannons.
Witnesses quoted by AFP and the Reuters news agency said protesters targeted and set fire to the offices of the UN telecommunications building as police tried to remove them from the site.
Thousands of security personnel were deployed in Geneva, about 50 kilometers (30 miles) southwest of Evian, ahead of the protest organized by the G7 opposition coalition.
G7 protests not allowed in France
About 20,000 people gathered for the march that started peacefully in the afternoon before violence erupted.
Some protesters tore through plywood panels installed to protect stores and broke windows, threw projectiles at police and set a Tesla on fire.
The Geneva city government said the demonstration was taking place in Geneva because France had refused to issue a permit for protests near the site of the G7 summit.
Protests are common at G7 gatherings, with demonstrators at the summit often expressing anger over capitalism, globalization, inequality and other issues.
Leaders of the Group of Seven rich nations, including US President Donald Trump, are scheduled to gather in Evian on Monday for a three-day meeting.
The war in the Middle East and Ukraine is expected to dominate the agenda.
Edited by: Jennifer Cimino Gonzalez
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