KYIV, Ukraine >> Air alerts sounded again and again in Kyiv and residents headed to shelters early Thursday morning, as a massive Russian attack on at least six cities across Ukraine killed at least two people and started fires, wounding at least 21 and trapping possibly dozens of people under rubble.

The early morning missile attack was Russia’s largest since August 15, and came a day after reports of sabotage at a Russian military airfield in Chkalovsk near Moscow.

It also coincided with the United Nations General Assembly summit in New York, where Ukrainian President Volodymyr Zelensky delivered a speech and presented a Ukrainian “peace formula,” and came on the International Day of Peace.

The same day, Poland said it would stop transferring its own weapons to Ukraine as it works to modernize its own military.

Polish Prime Minister Mateusz Morawiecki said the decision was not related to a temporary ban on Ukrainian grain imports, nor would it affect weapons transfers through Poland.

A dispute about whether Ukrainian grain should be allowed to enter the domestic markets of Poland and other European Union countries has pushed the tight relationship between Kyiv and Warsaw to its lowest point since Russia invaded Ukraine last year.

“We are no longer transferring any weapons to Ukraine because now we will arm ourselves with the most modern weapons,” he said in an interview on the private TV broadcaster Polsat News late Wednesday.

Morawiecki stressed that Poland would defend its economic interests but added that the dispute over grain imports would not hurt Ukraine’s security. He said a NATO and U.S. hub in the Polish city of Rzeszow used for transporting weapons into Ukraine would not be affected.

“We are not going to risk the security of Ukraine,” he said. Poland has transferred large amounts of its older weapons to Ukraine and has been upgrading its own inventory with new equipment purchased from South Korea and other countries.

In the southern Ukrainian city of Kherson, near the front lines, two people were killed Thursday and at least five injured after a strike hit a residential building, said regional Governor Oleksand Prokudin.

Seven people were injured in Kyiv, including a 9-year-old girl, reported Mayor Vitalii Klitschko, and some residential and commercial buildings were damaged.

At least six strikes hit the Slobidskyi district of Kharkiv, damaging civilian infrastructure, said regional Governor Oleh Syniehubov. The city’s mayor added that two people had been sent to hospitals.

At least 10 people were injured and at least one person was rescued from under rubble in Cherkasy, in central Ukraine, according to Ihor Klymenko, minister of internal affairs of Ukraine. Up to 23 people may still be buried under rubble in Cherkasy after the morning strike, said Cherkasy regional Governor Ihor Taburets. Rescue services were working to clear the debris.

An industrial zone was hit in the western region of Lviv, damaging buildings and starting a fire, but no information on casualties was immediately available, Klymenko added.

Regional Governor Vitalii Koval reported strikes in the city of Rivne in the northwest region of the same name, without immediately providing details.

Russia’s Ministry of Defence said 22 drones were taken down overnight by air defense systems, 19 above Russian-annexed Crimea and three others in the Kursk, Belgorod and Oryol regions near Ukraine. The defense ministry did not say whether there were any casualties.