ATHENS, Greece - A small group of self-proclaimed anarchists hurled firebombs at police patrolling in central Athens early Sunday, authorities said. No injuries or damage were reported.

Police said the attack happened at 3 a.m. in the tourist area of Monastiraki near the Acropolis, where police forces have been positioned for the past few weeks to secure the Athens Olympics.

Officers used tear gas to push back the anarchists, who then retreated after throwing rocks and setting fire to trash cans along the road. A small "battle" continued in the streets of Psiri till 4 a.m.

The incident came after two days of street rallies by anti-globalization and leftist groups in protest of a planned visit this weekend by U.S. Secretary of State Colin Powell. On Saturday, the State Department said Powell had canceled his visit.

Greece has spent a record $1.5 billion on security to protect the first Summer Games held since the Sept. 11, 2001 terrorist attacks. The games' closing ceremony is Sunday night.