Updated

Several hundred demonstrators are gathered in a Moscow park, trying to move to the nearby presidential administration building to present letters calling on President Vladimir Putin not to run for a fourth term in office in 2018..

The demonstration is one of about two dozen called for Saturday by Open Russia, an organization founded by Mikhail Khodorkovsky, the Putin critic and former oil tycoon who spent a decade behind bars before being pardoned in 2013.

The Moscow gathering was not sanctioned by officials, but there were no immediate reports of arrest. An Associated Press reporter at a similar demonstration in St. Petersburg saw about a dozen arrests and the OVD-Info group that monitors political repression said 16 people were detained in the Siberian city of Kemerovo.