More than 100 youth were detained after clashes with riot police and five Italians and four Greeks were arrested, reports said on Saturday.
The clashes come a day before the first anniversary of a police shooting of a teenager, which sparked the country's worst riots in decades.
The arrests and detentions took place after police were attacked with petrol bombs in central Athens and dozens of cars were set ablaze following a rally near the site where the teenager was shot Dec 6, 2008.
Two police officers were injured and rushed to hospital Friday after clashing with anarchists.
Since last year's death, Greece has been plagued by violence, including bombings, shootings and arson, targeting banks and multinationals.
Fearing a repeat of last year's rioting that caused millions of euros in damage, more than 10,000 officers have been deployed throughout downtown Athens ahead of the Dec 6 anniversary and planned marches.
Police said they would implement a "zero tolerance attitude" in dealing with the demonstrations planned for Sunday, which include a march through the city centre and memorial service at the makeshift shrine at the site of the shooting in Exarchia.
Reports said 150 foreigners had arrived from Italy, France and Spain ahead of the anniversary.