The United States has warned Russia that it would be a "grave mistake" to embark on military intervention in Ukraine.
"I don't think there should be any doubt whatsoever that any kind of military intervention that would violate the sovereign territorial integrity of Ukraine would be a huge - a grave mistake," US Secretary of State John Kerry said.
More top news
The group paid tribute in the Mamayev Kurgan memorial park.
A nine-year-old schoolgirl was among the victims around the city of Osaka.
Supporters are still arriving in the city.