A Ukrainian drone strike killed two people in Russia's southwestern Samara region, the governor said, as both sides continue to trade attacks with no end to the war in sight.
"The Ukrainian armed forces are attacking the city of Syzran with drones," wrote Vyacheslav Fedorishchev on Telegram, giving the toll of two dead.
People were also wounded in the attack on Syzran, which is home to a major oil refinery, according to Mr Fedorishchev.
Claiming fair retaliation for the Russian army's near-daily bombardments of Ukrainian cities across the four-year conflict, Ukraine has regularly launched attacks inside Russia, including on areas thousands of miles away from its territory.
Ukraine insists it targets Russian military sites, as well as energy installations in a bid to disrupt the fossil fuel revenues Moscow uses to fund the offensive.
Diplomatic efforts led by the US to end the conflict have been deadlocked, especially with the United States' attention diverted to the war against Iran since late February.
Ukrainian President Volodymyr Zelensky, in an overnight address, said there has recently been productive contact with the US.
"If, in the coming weeks, we manage to return to meaningful trilateral communication and involve the Europeans, this would be the right outcome," Mr Zelensky said.
"For our part, we are ready for such steps. I count on our partners to be ready as well - and that the Russians will not hide."
Meanwhile, Russia delivered nuclear munitions to field storage facilities in Belarus as part of major nuclear drills, the Russian Defence Ministry said.
The three-day nuclear exercise started on Tuesday and is taking place across Russia and Belarus.
"As part of the nuclear forces exercise, nuclear munitions were delivered to the field storage facilities of the missile brigade's position area in the Republic of Belarus," the ministry said.
Russia said the missile unit in Belarus was carrying out training to receive special munitions for the mobile Iskander-M tactical missile system, including loading munitions onto launch vehicles and secretly moving to a designated area for launch preparation.
Footage released by the Defence Ministry showed a truck driving through a forest amid lightning and unloading an item. It was not immediately clear what they were unloading.
The Iskander-M, a mobile guided missile system code-named"SS-26 Stone" by NATO, replaced the Soviet "Scud". Its guided missiles have a range of up to 500km and can carry conventional or nuclear warheads.
Throughout the war in Ukraine, President Vladimir Putin has issued reminders of Russia's nuclear might as a warning to the West not to go too far in its support of Kyiv.
The Kremlin slammed remarks by Lithuania's top diplomat as "verging on insanity" yesterday after Foreign Minister Kestutis Budrys said NATO had to show Moscow it was capable of penetrating the Russian exclave of Kaliningrad.
Kaliningrad is sandwiched between NATO members Lithuania and Poland on the Baltic coast. It has a population of around 1million and is heavily militarised, serving as the headquarters of Russia's Baltic Fleet.
