Many expressed fear for their own safety after the assassination of one of Vladimir Putin’s harshest critics.
Nemtsov, who was among leaders planning an opposition rally for Sunday, was shot on a bridge in the heart of Moscow.
Ukraine depends heavily on Russian natural gas and is a key gateway for shipments to Europe.
The dramatic act was a reminder of the stakes for both sides amid new East-West tensions.
Continuing rebel attacks in the east are preventing a withdrawal of heavy arms, key under a cease-fire deal.
Despite a cease-fire, Moscow continues its “land-grabbing,” secretary of state says in London.
Rebels said Thursday they would continue to “purge” their newly won territory of government soldiers.
The president’s call for an international peacekeeping mission after Ukrainian troops retreated from a key hub was a stark admission that government forces can’t repel pro-Russian rebels.
Heavy shelling Saturday called into question the viability of the peace deal that took effect at 12:01 Sunday.
Kiev says it lost soldiers overnight in the conflict-torn east, in the hours after a peace deal was reached.