KYIV, Ukraine (AP) — Waves of explosives-laden suicide drones struck Ukraine’s capital Monday, setting buildings ablaze, tearing a hole in one of them and sending people scurrying for cover or trying to shoot them down in what the president said was Russia’s attempt to terrorize civilians.

The concentrated use of the kamikaze drones was the second barrage in as many weeks — after months in which air attacks had become a rarity in central Kyiv. The assault sowed fear and frayed nerves as blasts rocked the city. Energy facilities were struck and one drone largely collapsed a residential building, killing four people, authorities said.

Intense bursts of gunfire rang out as the Iranian-made Shahed drones buzzed overhead, apparently as soldiers tried to destroy them. Others headed for shelter, nervously scanning the skies. But Ukraine has become grimly accustomed to attacks nearly eight months into the Russian invasion, and city life resumed as rescuers picked through debris.

Previous Russian airstrikes on Kyiv were mostly with missiles. Analysts believe the slower-moving Shahed drones can be programmed to accurately hit certain targets using GPS unless the system fails.

Also Monday, a Russian Su-34 warplane crashed in a residential area in the Russian port of Yeysk on the Sea of Azov after an engine failure, killing at least four people on the ground, injuring 25 others and starting a fire that engulfed several floors of a nine-story apartment building, authorities said. Six people were reported missing. Both crewmembers, on a training mission, bailed out safely, the Russian Defense Ministry said.

In Kyiv, Mayor Vitali Klitschko said Monday’s barrage came in successive waves of 28 drones — in what many fear could become a more common mode of attack as Russia seeks to avoid depleting its stockpiles of long-range precision missiles.

Five drones plunged into Kyiv itself, said Prime Minister Denys Shmyhal. In the Kyiv region, at least 13 were shot down, all flying in from the south, said Yurii Ihnat, a spokesman for Ukraine’s air force.

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. Four bodies were recovered, including those of a woman who was 6 months pregnant and her husband, Klitschko said. An older woman and another man also were killed there.

An Associated Press photographer caught one of the drones on camera, its triangle-shaped wing and pointed warhead clearly visible against the blue sky.

“The whole night, and the whole morning, the enemy terrorizes the civilian population,” Ukrainian President Volodymyr Zelenskyy said in a social media post. “Kamikaze drones and missiles are attacking all of Ukraine.”

“The enemy can attack our cities, but it won’t be able to break us,” he wrote.

Andrii Yermak, head of the presidential office, posted on social media that Shahed drones were used.

Zelenskyy, citing Ukrainian intelligence services, alleges Russia ordered 2,400 drones from Iran. Russia has rebranded them as Geran-2 drones — “geranium” in Russian. A photo of debris from one of Monday’s strikes, posted by Klitschko, showed “Geran-2” marked on a mangled tail fin.

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.

The drones pack an explosive charge and can linger over targets before nosediving into them. Their blasts jolted people awake, including Snizhana Kutrakova, 42, who lives near one of the strikes.

“I’m full of rage,” she said. “Full of rage and hate.”

The Russian military said it used “long-range air- and sea-based high-precision weapons” to strike Ukrainian military and energy facilities. They hit “all assigned targets,” Defense Ministry spokesman Igor Konashenkov said.

Ukrainian Foreign Minister Dmytro Kuleba called for European Union sanctions on Iran for providing drones to Russia and reiterated Ukraine’s need for air defenses and ammunition.

EU foreign policy chief Josep Borrell said the 27-nation bloc is gathering evidence about Iran’s drone sales to Russia, and if true, “we will be ready to react with the tools at our disposal.” The EU also approved a military training program in Europe for thousands of Ukrainian troops and plans for about 500 million euros ($486 million) in extra funds to buy weapons for Ukraine.

Iranian-made drones have been used elsewhere in Ukraine in recent weeks against urban centers and infrastructure, including power stations. At just $20,000 apiece, the Shahed is only a fraction of the cost of higher-tech missiles and conventional aircraft. The Kalibr cruise missile that Russia has used widely in Ukraine costs the military about $1 million each.

Drone swarms also challenge Ukrainian air defenses. Western nations have promised systems that can shoot down drones but much of that weaponry has yet to arrive and could be months away.

“The challenges are serious because the air defense forces and means are the same as they were at the beginning of the war,” said Ihnat, the air force spokesman. Some Western-supplied air defense weaponry can only be used during daylight hours when targets are visible, he added.

Russia forces also struck energy infrastructure elsewhere, apparently seeking to compound pressure on Kyiv’s government after previous attacks knocked out power supplies.

Shmyhal, the prime minister, said hundreds of settlements were without power after missile attacks in the Dnipropetrovsk and Sumy regions.

Ukraine’s nuclear operator said Russian shelling cut power again to the Zaporizhzhia Nuclear Power Plant, one of the most worrying flashpoints of the Russian invasion. The nuclear plant, Europe’s largest, needs power for critical safety systems. When shelling severs its power supply lines, the plant is forced to rely on diesel generators -– a temporary stopgap.

Russian President Vladimir Putin had said Friday that there was no need for more widespread attacks against Ukraine — after an earlier barrage of strikes that he said were retaliation for the bombing of a bridge connecting Ukraine’s Russian-occupied Crimean Peninsula with Russia.

However, Putin also said seven of 29 targets designated after the bridge attack were not hit “the way the Defense Ministry had planned,” so Moscow’s forces would continue to target them. He didn’t elaborate.

After months in which strikes in central Kyiv were rare, recent attacks put the country and its capital back on edge.

Monday’s strike on Kyiv came amid intensified fighting in the eastern regions of Donetsk and Luhansk, as well as a continued Ukrainian counteroffensive in the south near Kherson and Zaporizhzhia. Zelenskyy said Sunday there was heavy fighting around the cities of Bakhmut and Soledar in the Donetsk region.

The Donetsk and Luhansk regions make up the industrial east known as the Donbas, and were two of four regions annexed by Russia in September in defiance of international law.

In the south, Ukrainian air forces reported shooting down nine drones in the Mykolaiv region and six in the Odesa region. The governor of the eastern Kharkiv region said overnight attacks on a city and villages killed one and injured four.

Russia and Ukraine also completed a prisoner swap Monday, according to the Russian Defense Ministry. It said 110 Russians who were freed included 72 seamen from commercial vessels held since February, while 108 female Ukrainian POWs were handed over to Kyiv authorities, with two saying they wanted to stay in Russia. The Ukrainian side confirmed the exchange but not that two Ukrainians decided to stay in Russia.