Russia has held a huge parade to mark 69 years since the Soviets defeated the Nazis, amid a surge of patriotism over the annexation of Crimea from Ukraine.
President Vladimir Putin said it was a day when "patriotism triumphs", and vowed to defend the motherland.
Unconfirmed reports say Mr Putin will visit a parade in Crimea later.
Meanwhile, several people are reported to have been killed in a shoot-out between Ukrainian troops and separatists in the town of Mariupol.
Kiev recently recently launched an operation to retake official buildings occupied by pro-Russia rebels in Mariupol and several other cities in Ukraine's east and south.
Video footage from Mariupol showed armoured vehicles with Ukrainian flags in the streets, with the sound of gunfire in the background.
Soviet 'iron will'
Ukraine's interim authorities earlier said the Soviet victory would be marked with a low-key wreath-laying ceremony.
The Kiev authorities feared that pro-Russian activists would try to stoke violence if there were any higher profile celebrations.
Mr Putin did not mention Ukraine in his speech, instead stressing how the "iron will of the Soviet people" had saved Europe from slavery.
He told the crowd that 9 May, known as Victory Day in Russia, was a "day of grief and eternal memory".
"It is a holiday when an overwhelming force of patriotism triumphs, when all of us feel particularly acutely what it means to be loyal to the motherland and how important it is to defend its interests," he said.
German Chancellor Angela Merkel said it would be a pity if Mr Putin were to use the commemorations to visit Crimea.
The parade in Moscow traditionally features a display of military hardware and a show of patriotic fervour on Red Square.
The scope of this year's event was bigger than usual:
- The parade lasted 59 minutes, compared with its usual 45 minute running time
- Fifty more military vehicles were on display compared with last year
- The Sevastopol-based Black Sea Fleet played a larger role
Nazi Germany invaded the USSR - which included Ukraine - in June 1941 and advanced almost as far as Moscow before being driven back to Berlin in some of the fiercest fighting of the war.
Russia estimates that 26.6 million Soviet citizens were killed in the war, about 8.7 million of them members of the armed forces.
In south and eastern Ukraine, pro-Russian separatists have said they will go ahead with independence referendums on Sunday.
Mr Putin had called for the referendums on autonomy to be postponed to create the conditions for dialogue.
Activists remain in control of many official buildings across the south and east despite a military operation by Kiev to remove them. Dozens of people have been killed in the unrest.
Ukraine is preparing for elections on 25 May following the ousting of pro-Russian President Viktor Yanukovych in February by pro-Western protesters.