Riot police used tear gas and rubber bullets to beat back a crowd of several hundred anti-NATO protesters in Strasbourg on Thursday as the city in eastern France, host of the alliance's 60th anniversary summit, readied for the arrival of world leaders. Police lobbed hundreds of tear gas canisters during clashes between about 40 riot police and some 200 masked protesters in the neighborhood of Neuhoff, in the southern part of the city near the German border. The masked protesters had been among a crowd of about 800 demonstrators when they broke away and repeatedly pelted officers with rocks and bottles. There were no immediate reports of injuries. Police said a dozen protesters were arrested. At one point, protesters set fire in the middle of a street to building materials they had scooped up from a nearby construction site. By late Thursday, calm had returned to Strasbourg, but two more full days of planned protests lie ahead.