Sergei Marchenko, a representative of the Moscow prosecutor's office, said the Saturday afternoon attack on the two men, aged 23 and 26, was "a result of a conflict with a group of 17- and 18-year-olds."
Police said they had taken a resident of central Russia into custody in connection with the assault. "The detained 24-year-old resident of Lipetsk is suspected of attacking two Armenians," a spokesman said. "The suspect was on the wanted list already."
The spokesman said police was checking another group of people suspected of involvement in the attack.
"Investigators know their names and other details," he said.
Marchenko said the Moscow subway prosecutors had agreed to launch an inquiry into hooliganism, a charge often brought against suspects in assaults and similar incidents.
It is still unclear whether the incident was another attack in a series of race-hate crimes that have recently rocked the country.
The city of Voronezh in central Russia has seen at least seven apparently racially motivated killings of non-white foreigners over the past six years, including the murder of a Peruvian student last October.
St. Petersburg has been suffering from negative publicity over alleged neo-Nazi attacks and murders, including the killing of a student from Senegal in April and the stabbing of a nine-year-old girl of mixed Russian-African origin in early 2006.
In an effort to combat these extremist and xenophobic trends, Russia set up a nationwide public movement, Our Russia, in late June. The movement comprises politicians, entrepreneurs, figures from the arts world and human rights activists, who will work closely with all of Russia's religious and cultural communities.