"I just heard from the top military leadership of the country that a battle is ongoing right now, for our historical lands, for our people," Putin said.
In a short address to the tens of thousands gathered at Moscow's main Luzhniki stadium, Putin also praised Russian servicemen in Ukraine who are "fighting heroically, courageously, bravely: we are proud of them".
The audience, waving Russian flags, braved cold winter temperatures of -15 degrees Celsius, were attending the "Glory to the Defenders of the Fatherland" concert, held on the eve of the eponymous Russian public holiday.
It also comes two days before the anniversary of the Ukraine offensive.
Rock star Grigory Leps opened the show with a song in honor of Russia, with images of "The Motherland Calls" statue in the southern city of Volgograd displayed on screens around the stadium.
Organizers brought on stage children from the Ukrainian Donbas, including from the port city of Mariupol, which was devastated by a long siege before Russia captured it.
Ukraine has accused Russia of kidnapping thousands of Ukrainian children from territories it controls, something Moscow has denied, insisting it organized legal adoptions.
Officials from the Ukrainian regions that Moscow claims to have annexed were also at the stadium and spoke to Russian state-run media.
"The West is an accomplice to (Ukrainian) war crimes" said Denis Pushilin, the Kremlin-appointed leader of the Donetsk region. He reiterated Moscow's claims of "Nazi ideology" governing the Ukrainian government.
Putin alleged that the treatment of Russian speakers in the country is comparable with the actions of Nazi Germany when he launched his special military operation there.
He has blamed the escalation of the Ukraine conflict on Western capitals, which have backed Kyiv financially and militarily.
After facing, a series of humiliating defeats on the battlefield, the Kremlin has started to characterize its offensive as a wider conflict against the West, the equivalent of the "Great Patriotic War" against Nazi Germany.