President Vladimir V. Putin began to deliver a wide-ranging speech on Thursday that was expected to offer an opportunity to gauge the Russian’s leader’s appetite for escalating the war in Ukraine to avoid defeat.
Mr. Putin’s remarks on Thursday at the Valdai Discussion Club, a Kremlin-affiliated research institute, came a day after he became the most senior Russian official to make unsubstantiated claims that Ukraine was preparing to use what is known as a dirty bomb.
Western governments have dismissed the claims as false and warn that they could be a pretext for Russia to use tactical nuclear weapons.
The Kremlin’s spokesman, Dmitri S. Peskov, told reporters on Wednesday that the Valdai speech would be an important event. “There will be an extensive speech; there will be a discussion,” he said.
The Valdai plenary session has traditionally served as one of the most extensive windows into the Russian president’s view on foreign affairs and geopolitics. It is often a rare moment of unscripted questioning from independent analysts and journalists, including those from the West. Mr. Putin is expected to join the session in the evening Moscow time.
On Wednesday, in a video address to intelligence chiefs from former Soviet states, Mr. Putin said that the risk of conflict was high in the region and around the world. “It is also known about plans to use a so-called dirty bomb for provocation,” he said.
President Biden warned Mr. Putin on Tuesday that it would be “an incredibly serious mistake” to use a tactical nuclear weapon in the conflict. “I’m not guaranteeing you that it’s a false flag operation yet — don’t know — but it would be a serious, serious mistake,” he said.
Using disinformation and propaganda is a key part of Mr. Putin’s playbook. At the start of the invasion, Russia spread disinformation about a purported need to stamp out Nazism in Ukraine. But in recent days Moscow’s propaganda has shifted.
On social media and in the news, Russia maintains that it is working to stop terrorism. Falsely accusing Ukraine of planning a dirty bomb attack serves that narrative. FilterLabs, a company that tracks public sentiment in Russia and elsewhere, noted a surge this week in discussions about nuclear terrorism by Ukraine.
By framing Ukraine as the potential nuclear aggressor, Russia can raise tensions without setting off a backlash from its population or further undermining support for Mr. Putin.
Julian E. Barnes and Carole Landry contributed reporting.