Updated

MOSCOW (AP) — Four EU lawmakers visiting Russia have attended an opposition rally in central Moscow and criticized police for arresting its organizer.

Heidi Hautala, who heads the EU parliament's subcommittee on human rights, called the arrest of former Russian Prime Minister Boris Nemtsov at Tuesday's rally "a violation."

Police heavily cordoned off the square where it was held.

Opposition groups have been calling rallies on the 31st day of the month in recognition of the 31st article of the Russian Constitution, which guarantees the right of assembly.

Most of rallies have been banned or dispersed by police.

The EU lawmakers traveled to Russia to attend a commemoration ceremony for the hostage-taking raid on a school in Beslan, Russia, in 2004.