KYIV, Ukraine (AP) — Ukraine’s capital came under a large-scale Russian drone and missile attack overnight and into early Saturday that left at least 15 people injured, according to Ukrainian officials. Explosions and machine gun fire wre heard throughout Kyiv as many sought shelter in subway stations.

The attack came hours after Russia and Ukraine began a major prisoner exchange of hundreds of soldiers and civilians, the first phase of a swap agreed on by the two sides at a meeting in Istanbul last week.

The agreement was a rare moment of cooperation in otherwise failed efforts to reach a ceasefire in the 3-year-old war.

‘A difficult night’

Russia attacked Ukraine with 14 ballistic missiles and 250 Shahed drones overnight, officials said, adding that Ukrainian forces shot down 6 missiles and neutralized 245 drones — 128 drones were shot down and 117 were thwarted using electronic warfare.

The Kyiv City Military Administration said it was one of the most massive combined missile and drone attacks on the capital.

“A difficult night for all of us,” the administration said in a statement.

The debris of intercepted missiles and drones fell in at least six city districts of the Ukrainian capital. According to the acting head of Kyiv's military administration, Tymur Tkachenko, six people required medical care after the attack and two fires were sparked in the Solomianskyi district of Kyiv.

The Obolon district, where a residential building was heavily damaged in the attack, was the hardest hit. There were at least five wounded in the area, the administration said.

Yurii Bondarchuk, a local resident, said the air raid siren “started as usual, then the drones started to fly around as they constantly do.”

Moments later, he heard a boom and saw shattered glass fly through the air.

“The balcony is totally wiped out, as well as the windows and the doors,” he said, describing the damage to his apartment as he stood in the dark of the night, smoking a cigarette to calm his nerves while firefighters worked to extinguish the flames.

The air raid alert in Kyiv lasted more than seven hours, warning of incoming missiles and drones.

Kyiv's mayor, Vitalii Klitschko, warned residents ahead of the attack that more than 20 Russian strike drones were heading toward the city. As the attack continued, he said drone debris fell on a shopping mall and a residential building in Obolon district of Kyiv. Emergency services were headed to the site, Klitschko said.

A complex deal

The prisoner swap on Friday was the first phase of a complicated deal involving the exchange of 1,000 prisoners from each side.

Ukrainian President Volodymyr Zelenskyy said the first phase of the deal brought home 390 Ukrainians, with further releases expected over the weekend, which will make it the largest swap of the war. Russia’s Defense Ministry said it received the same number of people from Ukraine.

The swap took place at the border with Belarus, in northern Ukraine, according to a Ukrainian official who spoke on condition of anonymity because he was not authorized to speak publicly.

The released Russians were taken to Belarus for medical treatment, the Russian Defense Ministry said.

However, the exchange — the latest of dozens of swaps since the war began and the biggest involving Ukrainian civilians so far — did not herald a halt in the fighting.

Battles continued along the roughly 1,000-kilometer (620-mile) front line, where tens of thousands of soldiers have been killed, and neither country has relented in its deep strikes.

After the May 16 Istanbul meeting, Turkish Foreign Minister Hakan Fidan called the prisoner swap a “confidence-building measure” and said the parties had agreed in principle to meet again.

But Kremlin spokesman Dmitry Peskov said on Friday that there has been no agreement yet on the venue for the next round of talks as diplomatic maneuvering continued.

Russian Foreign Minister Sergey Lavrov said Moscow would give Ukraine a draft document outlining its conditions for a “sustainable, long-term, comprehensive” peace agreement, once the ongoing prisoner exchange had finished.

European leaders have accused Russian President Vladimir Putin of dragging his feet in peace efforts while he tries to press his larger army’s battlefield initiative and capture more Ukrainian land.

The Istanbul meeting revealed that both sides remained far apart on key conditions for ending the fighting. One such condition for Ukraine, backed by its Western allies, is a temporary ceasefire as a first step toward a peaceful settlement.

Russia’s Defense Ministry said it had shot down 788 Ukrainian drones away from the battlefield between May 20 and May 23.

Ukraine’s air force said Russia fired 175 Shahed and decoy drones, as well as a ballistic missile since late Thursday.

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