Russian Security Council Deputy Chairman Dmitry Medvedev said the only real threat the world should worry about is World War III, Reuters and TASS reported, quoted by BTA.
Medvedev's reaction came after US President Donald Trump criticized Russian leader Vladimir Putin.
"Regarding Trump's words that Putin is "playing with fire" and that "really bad things" could happen to Russia — I only know of one really bad thing — World War III. "I hope Trump understands," Medvedev wrote on the social network "Ex".
Earlier, Trump warned Vladimir Putin that he was "playing with fire", attacking his Russian counterpart for the stagnation in efforts to end the war in Ukraine.
"What Vladimir Putin doesn't realize is that if it weren't for me, a lot of really bad things would have already happened to Russia, and I mean really bad. "He is playing with fire!", Trump wrote on the social network "Truth Social".
Russian forces have seized four border villages in the northeastern Sumy region of Ukraine, a local official said on Tuesday, quoted by BTA, days after Russian President Vladimir Putin said he had ordered troops to create a buffer zone along the border.
Sumi borders Russia's Kursk region, where a surprise Ukrainian incursion last year seized a small area of the region, the first occupation of Russian territory since World War II. Putin says the long border is vulnerable to Ukrainian incursions and creating a buffer zone could help Russia prevent further cross-border attacks.
A year ago, the Russian president said another Russian offensive since then was aimed at creating a buffer zone in Ukraine’s northeastern Kharkiv region. That could help protect Russia’s border Belgorod region, where frequent Ukrainian attacks have troubled the Kremlin.
Meanwhile, Russia’s bombing campaign, which has escalated in recent days, slowed overnight Tuesday, with far fewer Russian drones targeting Ukrainian cities.
Moscow’s invasion shows no sign of abating despite months of intense U.S.-led efforts to secure a ceasefire and advance peace talks. Since Russian and Ukrainian delegations met in Turkey on May 16 for their first direct talks in three years, the only tangible result has been a major prisoner swap, but the talks have not produced a significant breakthrough.
US special envoy for Ukraine Keith Kellogg said Putin had yet to deliver the promised memorandum, which the Russian leader told US President Donald Trump in a phone call on May 19 would outline the framework for a possible peace deal.
The Kremlin has also ruled out the Vatican as a venue for talks, he said. "We really wanted to have it in the Vatican, but the Russians didn't want to go there, so I think Geneva could be the next stop," Kellogg told Fox News.
Turkish Foreign Minister Hakan Fidan said his country was also ready to host a new round of peace talks.
From Friday to Sunday, Russia launched about 900 drones into Ukraine, officials said, amid a series of large-scale bombings. On Sunday night, Russia launched its largest drone attack of the three-year war, launching 355.
On Monday and Tuesday, Russia launched 60 drones into Ukraine, the Ukrainian air force said. Russia's Defense Ministry said its air defense systems shot down 99 Ukrainian drones overnight over seven Russian regions.
A sharp increase in Russian bombing over the weekend prompted a rebuke from Trump, who said Putin had "gone crazy." The comment drew a sharp response from the Kremlin on Monday, with spokesman Dmitry Peskov criticizing "emotional reactions" of the events.
On Monday, he took a softer tone, welcoming U.S. peace efforts and saying that "the Americans and President Trump have taken a fairly balanced approach."
In Sumy region, Russian forces are trying to advance deeper after capturing some villages, said Oleg Grigorov, head of the Sumy regional military administration.
Ukrainian forces are trying to hold their positions, he said, adding that villagers had been evacuated earlier and there was no immediate threat to civilians.