MOSCOW — Hundreds of people were arrested in the center of Moscow while trying to gather Sunday for an unauthorized demonstration called by an extreme nationalist group.

The arrests at Manezh Square, adjacent to the Kremlin, came two days after Russia’s domestic security agency said it had arrested some of the group’s members. They are suspected of planning to firebomb administrative buildings.

The group, called Artpodgotovka, was declared an extremist group by a Russian court last week. Its exiled leader, Vyacheslav Maltsev, had called for protests to force President Vladimir Putin’s resignation.

The OVD-Info organization that monitors political arrests said 376 people were detained Sunday in Moscow and another 36 in three other cities.

Analyst Stanislav Belkovsky suggested that the large number of arrests exaggerated any potential threat posed by the nationalist movement.

‘‘Special services must constantly create threats, so that they have something to neutralize,’’ he said on independent radio station Ekho Moskvy.

In a separate development, last week, court officials confirmed that Russian opposition leader Alexei Navalny is suing Putin over authorities’ repeated refusals to sanction rallies for his supporters.