Videos of attack drones flying ominously in Ukrainian airspace and slamming into buildings have been shared widely on social media. These drones, defence experts say, are Iranian-made "loitering munitions" Shahed-136, also known as Geran-2 in the Russian military.
Rob Lee, a defence researcher who has been closely following the war in Ukraine, has tweeted several videos of what appears to be Geran-2 loitering munitions flying over Ukraine's capital Kyiv and the eastern region of Sumy.
The videos show the attack drones flying in eerie silence as they home in on their targets. Ukrainians tweeted photos of burning apartments and condemned the drone attacks, which they say hit civilian infrastructure.
Another video shows what appears to be a small shoulder-fired missile being shot at an incoming drone. The drone, however, hits the target, as indicated by a huge fireball moments after the missile was fired to intercept the Geran-2.
Another footage claims to show a Geran-2 being shot down.
Loitering munition, as the name suggests, loiters above an area, identifies a target and hits it. Such a weapon comes in all shapes and sizes, from the size of a shoebox to a surfboard.
Ukrainian authorities have said six people were killed by the Russian drone attacks in Kyiv and Sumy.
"As of now, the number of people killed as a result of a kamikaze drone attack on a residential building has increased to three. 19 people have been rescued. (Rescue) work is ongoing," the deputy head of the presidency, Kyrylo Tymoshenko, said on social media.
Kyiv mayor Vitali Klitschko said two of the people killed in the capital were a young married couple. "A husband and wife who were expecting a child. The woman was six months pregnant," he said on social media, news agency AFP reported.