Russian President Vladimir Putin has attended a 70th anniversary memorial service for the victims of Soviet-era political repression at Butovo, just outside Moscow.
Mr Putin joined the congregation for the Russian Orthodox ceremony at the Church of New Martyrs. More than 20,000 prisoners were shot at Butovo between 1937-8.
In a speech outside, Mr Putin said the purges happened because "worthless ideals that seemed feasible domineered the main values - human life, human rights and freedoms".
He was joined by a priest whose grandfather was among those killed. Russian human rights group Memorial estimates 725,000 people died during the 1937-8 purges.
Stopping to view photos of the dead next to floral displays at the foot of a cross dedicated to the victims, Mr Putin said: "It seems incredible, madness."
The Russian president, a former KGB officer, was also joined at the service by Patriarch Alexy II, head of the Russian Orthodox Church.
Meanwhile, in Moscow flowers were laid on Lubyanka Square by the ex-KGB building, where rights activists accused Mr Putin of curtailing Russia's post-Soviet freedoms.