“These Russian patriots were met with a coordinated campaign of brutality and oppression from Russian authorities,” McCain said, citing news reports that some of the activists were “beaten bloody and dragged away by the police.”

Opposition movements and rights groups have organized similar demonstrations on the 31st day of months with 31 days, a nod to Article 31 of the Russian constitution that guarantees the right to public demonstrations.

“It is tragic that the criminalization of political discourse, and the enforcement of it through violence, continues today in modern Russia,” said McCain, President Barack Obama’s Republican rival for the White House in 2008.

The Arizona senator called for the “immediate release” of Nemtsov “and all who have been unfairly arrested in common cause with him” and pressed the Obama administration to help ensure the prisoners are freed.

Washington must “make it clear to the Russian government that continued violations of human rights will only harm our bilateral relationship,” said McCain.