Gangs of far-right youths attacked dark-skinned immigrants in central Athens and clashed with riot police Thursday, leaving at least 25 people injured, in a show of force by extremist groups.
The attacks, which lasted several hours, occurred following a downtown protest against a deadly mugging that had happened earlier in the week.
Several hundred youths, dressed in black and some wielding bats, were involved in the daytime attacks in an area where thousands of Asian and African immigrants live. Immigrants were chased through narrow streets of the city's Kato Patissia neighborhood and punched and kicked to the ground by groups of attackers.
Officials from a state-run Polykliniki and Athens General hospitals told the AP that 25 people were treated for injuries following the clashes _ 19 immigrants and six Greeks, with one man remaining overnight for observation.
Thursday's clashes followed a spike in racial attacks in Greece during its financial crisis and the election of the leader of a violent far-right Chrysi Avgi organization to Athens' City Council in November.
Police said 48 protesters were detained for questioning but none were immediately charged.
Human Rights Watch urged Greek authorities to conduct "a diligent investigation" and prosecute the violent offenders.
"It's horrifying. Clearly these are indiscriminate racist attacks in a city and a country that by all accounts has seen a troubling _ an alarming _ rise in racist sentiment and racist violence over the past several years," Judith Sunderland, a senior for researcher at the rights group for Western Europe told the AP.
Far-right and nationalist groups have seized on witness testimony that immigrants allegedly carried out the fatal stabbing on Tuesday of a man who was about to drive his pregnant wife to a hospital. Police have not identified any suspects.
A makeshift shrine with candles and flowers now stands at the site of the killing.
The far-right youths joined and eventually took over a peaceful demonstration from that site to Athens' City Hall, chasing and beating migrants as they marched through the city center. But most of the trouble occurred after the rally.
Thugs in motorcycle helmets beat up immigrants, sending others fleeing for safety amid heavy rush-hour traffic. Similar attacks have occurred over the past two days.
The black-clad ultranationalist youths marched through migrant areas, and running battles with riot police broke out as youths chased immigrants down side streets. Male and female protesters were seen taking part in the beatings.
Clashes with police broke out in a red-light district of the capital, where riot police fired volleys of tear gas, as women in closed-up brothels peered out of windows and balconies at the violence below.
The rioters taunted immigrant onlookers on apartment block windows and broke into chants of "Where are the foreigners now?" and "Jobs for Greeks only."
Also Thursday, police said they were investigating the fatal stabbing of a 21-year-old Bangladeshi man in a crime-ridden part of central Athens with a strong far-right presence. There have been no arrests, and the motive of the attack was unclear.
Greece is the EU's main entry point for illegal immigrants. Over the past few years, the capital's center has seen a major increase in migrant numbers, which, combined with worsening crime rates, has prompted a far-right backlash.
A government spokesman on Thursday condemned violence during frequent anti-government protests and the recent racial attacks, but could not be reached for further comment.
On Wednesday, 20,000 people marched through Athens to protest the Socialist government's painful austerity measures. Most of the protest was peaceful, but clashes occurred between petrol bomb- and stone-throwing anarchists and riot police. More than two dozen people were injured, including two police officers.
Greece has been grappling with a severe financial crisis for more than a year and was rescued from bankruptcy by a euro110 billion international bailout package in May 2010. In return, the government imposed strict austerity measures, including cutting public sector salaries, freezing pensions and increasing taxes.
But it has struggled to meet revenue targets during a recession, and the government is soon due to unveil new cutbacks aimed at saving an estimated euro23 billion ($33 billion) through 2015.
Nicholas Paphitis and Elena Becatoros in Athens contributed.