Greece has seen an increase in racist violence over the past year, with dark-skinned migrants attacked by groups of men armed with metal bars, knives and wooden bats. Tens of thousands of migrants have also been rounded up by police in a government crackdown on illegal immigration.
The country has also seen a rise in popularity of the extreme nationalist Golden Dawn party, which went from a fringe group in 2009 elections to win nearly 7 percent of the vote and 18 seats in the 300-member Parliament in June. The party advocates that all immigrants should be expelled, but denies its members have been involved in racist attacks.
In a security message, the embassy said the State Department's travel section had been "updated to inform U.S. citizens of a rise in unprovoked harassment and violent attacks against persons who, because of their complexion, are perceived to be foreign migrants. U.S. citizens most at risk are those of African, Asian, Hispanic, or Middle Eastern descent in Athens and other major cities."
The travel advice on Greece also said the embassy "has confirmed reports of U.S. African-American citizens detained by police authorities conducting sweeps for illegal immigrants in Athens."
Tourism is a major source of revenue in Greece, and the country is sensitive to any travel advice that might affect visitors. The country is struggling through a deep financial crisis that has left one in four Greeks out of work and the country facing a sixth year of a recession.
"Greece was and remains a safe country," Foreign Ministry spokesman Grigoris Delavekouras said in a statement. "The isolated incidents of racist violence which have occurred are foreign to Greeks, our civilization and the long tradition of Greek hospitality."
Delavekouras stressed that the government was "following a zero tolerance policy" against such incidents "and is taking all the necessary measures for the prevention and suppression of such behavior, which we condemn."
On Thursday, police said a 31-year-old Greek policeman had been arrested on suspicion of robbing migrants at gunpoint in a racially tense part of central Athens.
The muggings took place in the capital's Aghios Panteleimon district, home to thousands of immigrants from Asia and Africa—many of whom entered Greece illegally. The crime-ridden area has become a flashpoint of recent racist attacks, with gangs of ultranationalists smashing immigrants' shops and attacking dark-skinned people.