The Investigative Committee has launched a new probe against the mayor of Dagestan's main city of Makhachkala Said Amirov, accusing him of "preparing a terrorist act" and trafficking weapons, the committee said in a statement.
Investigators believe that Amirov and two of his associates, a prosecutor's aide from the town of Khasavyurt and a deputy mayor of the town of Kaspiysk, "were preparing to assassinate a government official in order to have an effect on decisions made by the Dagestan authorities".
Strela is a Soviet-made shoulder-fired missile system, or MANPAD, similar to the US-made Stinger, and widely used in regional conflicts.
Investigators said they also found "significant" evidence in Amirov's home which was searched.
Amirov is currently under arrest on charges of murder and has been stripped of his mayorship. He is accused of ordering the killing of senior investigator Arsen Gadzhibekov and running an organised crime group in Dagestan.
Amirov was a key figure in the region plagued by violence, a veteran official widely seen as untouchable, and the surprise arrest was seen by many as a shift in Kremlin policy in the North Caucasus.
Makhachkala, which made recent headlines as the home of the parents of the Tsarnaev brothers, suspects in the Boston Marathon attack, is a regular target of bombings and shootings, along with the rest of the unstable region.