Alexei Ozerov, a leading researcher at the Russian Academy of Sciences Volcanology and Seismology Institute's Far Eastern department, said many local earthquakes have occurred around the volcano since it last erupted February 15.
"The nature of the seismic activity makes it possible to assume with a high degree of probability that a secondary eruption of the volcano will begin soon, during which lava will flow from a fissure that has opened up on one of its slopes and powerful ash emissions will occur," he said.
Ozerov said such eruptions have not taken place for more than 15 years, but added that tourists and sportsmen should avoid the slopes of the volcano.
Prior to its February eruption, Klyuchevskoi last came to life in January-May 2005.
Eruptions do not immediately threaten the peninsula's settlements, but volcanic ash, consisting of magma particles with a diameter of up to 2 millimeters (.078 inches), can poison land and water. Ash emissions and trails can also present a danger to aircraft.