An investigation was opened after an altercation on January 9, when the Sudanese men aged 23 and 31 were at a bus stop with two Russian women. The group became involved in an exchange of words with two young local men, which then erupted into a fight.
The police arrested the two locals, who could have faced seven years in prison if they had been convicted.
The incident was one in a string that have prompted Russian and foreign human-rights groups to raise concerns over the alarming spread of racist and xenophobic attitudes in the country.
An African student was shot dead in St. Petersburg with a rifle marked with a swastika on April 7, and two Mongolian students were beaten up in the city's subway a week later. A 17-year-old Armenian was stabbed to death in the Moscow subway on Saturday, although police have sought to downplay the killing, saying it happened after an argument broke out.
