MOSCOW - Moscow's police chief questioned Wednesday whether civil liberties are even practical when authorities need to keep law and order, the latest sign that ethnic tensions in Russia could lead to new democratic rollbacks.

His remarks backed Prime Minister Vladimir V. Putin's comments on a possible restoration of strict Soviet-era restrictions on movement into big cities such as Moscow or St. Petersburg, a move that seems to target dark-complexioned people in the Caucasus.

Kremlin critics say that ethnic tensions are being deliberately fanned as a pretext to introduce repressive legislation ahead of Russia's 2012 presidential election. They say the measures floated by authorities could cripple attempts to hold peaceful antigovernment demonstrations.

A young Slavic soccer fan died this month in a fight with six men from the southern Caucasus, leading to a nationalist backlash that has spilled into racist violence on the streets. A protest outside the Kremlin saw thousands of Slavic hooligans chanting racist slogans, raising their hands in a Nazi salute, and beating nonwhites.

Police briefly detained thousands of nationalist protesters to head off further unrest and arrested the soccer fan's suspected killers.

On Wednesday, Moscow police chief Vladimir Kolokoltsev asked whether Russians' freedom of movement was partly to blame for the violence.

"All these problems are more difficult to solve compared to a time when a much tougher registration system was in place," he said.

President Dmitry Medvedev, in contrast, has suggested that participants in unauthorized rallies get a mandatory prison sentence rather than a fine and a warning.

After meeting with soccer fans Tuesday, Putin laid flowers at the grave of the slain fan, Yegor Sviridov, a member of Spartak Moscow's fan group. Some criticized the move, saying Putin was siding with a known extremist in Sviridov.

While ethnic Russians make up four-fifths of Russia's population of 142 million, the country is also home to about 180 ethnic groups.

The Caucasus region hosts at least 100 ethnicities including Chechens, who have waged two separatist wars against Moscow since the 1991 collapse of the Soviet Union.