Russia launched another large drone attack on Ukraine, striking Kyiv and damaging a maternity ward in the southern port of Odesa, regional officials said early on Tuesday.

The overnight attacks follow Russia’s biggest drone strike on Ukraine on Monday – part of intensified operations that Moscow said were retaliatory measures for Kyiv’s recent brazen attacks inside Russia.

Medics were called to four districts of Kyiv a couple hours after midnight on Tuesday, including the historic Podil neighbourhood, Mayor Vitali Klitschko said on the Telegram messaging app.

The military said the strikes were still ongoing and urged people to seek bomb shelters. The full scale of the attack was not immediately clear.

“Enemy drones are simultaneously attacking several districts of the city,” Timur Tkachenko, head of Kyiv’s military administration said on the Telegram messaging app. “There is damage to residential buildings and fires. Rescuers are working at the sites.”

Reuters’ witnesses heard a series of loud explosions throughout the city.

In the southern port of Odesa, a “massive” drone attack targeted an emergency medical building and a maternity ward, as well as residential buildings, Oleh Kiper, governor of the broader Odesa region said on Telegram.

Regarding the maternity hospital there were no casualties and patients and staff were evacuated, Kiper said. He posted photos of broken windows in what looked like a medical facility and of damages to facades of several buildings.

Both sides deny targeting civilians in the war that Russia launched against Ukraine more than three years ago. But thousands of civilians have been killed in the conflict, the chief majority of them Ukrainian.