The BBC's Russia editor saw Putin's flagship economic event overshadowed by Ukrainian drones attacks.
Russia launches 656 drones and 73 missiles at Ukraine overnight, according to Ukraine's air force.
Peace talks remain deadlocked as drones hit sites in Saudi Arabia and the UAE.
Russian authorities say three people killed in the Moscow region and one in Belgorod in Ukrainian attacks.
Ukraine's President Volodymyr Zelensky warns of "more waves" of Russian drone attacks on Wednesday.