Explosive suicide drones have been raining down on Ukraine’s capital in recent days, setting buildings on fire and forcing people to run for cover. It’s Russia’s latest tool targeting civilians in Kyiv.

Known as the Shahed-136, these self-destructing suicide drones are different from traditional military drones. They’re a lot smaller and are designed to crash into specific GPS coordinates.

The main advantage is that they’re hard to detect and can be fired from a distance of about 1,200 miles from their target location. The drones circle an area before making impact and detonate like a missile.

While Ukraine has shot down a few of them, at least five suicide drones have made impact in Kyiv. One strike appeared to target the city’s heating network, hitting an operations center. Another slammed into a four-story residential building, ripping open a gaping hole and collapsing at least three apartments, as reported by the Associated Press. Four bodies were recovered, including those of a woman who was six months pregnant and her husband, Kyiv Mayor Vitali Klitschko said. An older woman and another man also were killed there.

U.S. officials have confirmed the drones used in these recent attacks are Iranian made. Iran has previously denied providing Russia with weapons, although its Revolutionary Guard chief has boasted of providing arms to the world’s top powers, without elaborating.

Officials estimate Russia has ordered at least 2,400 of the Shahed-136 drones.

Despite billions of dollars in U.S. support to defend Ukraine, Ukraine President Volodymyr Zelenskyy said his nation has only 10% of what it needs to fend off Russian attacks from the sky.