UNITED NATIONS, May 27. /TASS/. UN Secretary-General Antonio Guterres is concerned about the Ukrainian drone attacks on Russia, the UN chief’s spokesman Stephane Dujarric said at a briefing. "The Secretary-General is also concerned about the impact of reported Ukrainian drone strikes on the civilian population in the Russian Federation. Attacks against civilians and attacks against civilian infrastructure are prohibited under international law," he said, adding that the organization "condemns all such attacks, wherever they occur." Dujarric has once again reiterated the UN chief’s call "for a full, immediate and unconditional ceasefire in Ukraine as a first step towards a just, comprehensive and sustainable peace." Earlier, the Russian Defense Ministry reported that Kiev had significantly stepped up drone and missile attacks on Russian facilities. Since May 20, Russian air defenses have downed 2,331 drones, including 1,465 outside the special military operation zone, the ministry pointed out.