Poland demanded an explanation from Russia on Sunday after one of its missiles strayed briefly into Polish airspace during a massive missile attack on Ukraine, prompting the NATO member to activate F-16 fighter jets.

The incident came as Russia launched its third massive missile attack on Ukraine in the past four days, and the second to target the capital of Kyiv.

The head of Kyiv's military administration, Serhiy Popko, said Russia used cruise missiles launched from Tu-95MS strategic bombers. An air alert in the capital lasted for more than two hours as rockets entered Kyiv in groups from the north.

He said the attacks were launched from the Engels district in the Saratov region of Russia.

According to preliminary data, there were no casualties or damage in the capital, he said.

Armed Forces Operational Command of Poland, a member of NATO, said in a statement that there was a violation of Polish airspace at 4:23 a.m. by one of the cruise missiles launched by Russia against towns in western Ukraine.

The object entered near Oserdów, a village in an agricultural region near the border with Ukraine, and stayed there for 39 seconds, the statement said.

Poland's Defense Minister Władysław Kosiniak-Kamysz later told reporters in a televised news conference that the Russian missile would have been shot down had there been any indication that it was heading towards a target in Poland.

He said that Polish authorities monitored the attack on Ukraine and was in contact with Ukrainian counterparts. Polish and NATO F-16s were activated as part of the strategic response.

He said the missile penetrated Polish airspace about a kilometer or two (0.6 miles to 1.2 miles) as Russia was targeting the region around Lviv in western Ukraine.

“As last night’s rocket attack on Ukraine was one of the most intense since the beginning of the Russian aggression, all the strategic procedures were launched on time and the object was monitored until it left the Polish air space,” he said.

On the diplomatic front, the Polish foreign ministry said it would “demand explanations from the Russian Federation in connection with another violation of the country’s airspace.”

“Above all, we call on the Russian Federation to stop the terrorist air attacks on the inhabitants and territory of Ukraine, end the war, and address the country’s internal problems,” the statement read.

Andrzej Szejna, a deputy foreign minister, told the TVN24 broadcaster that the foreign ministry intended to summon the Russian ambassador to Poland and hand him a protest note.

Henryk Zdyb, the head of the village of Oserdów, said in an interview with the daily Gazeta Wyborcza that he saw the missile, saying it produced a whistling sound.

“I saw a rapidly moving object in the sky. It was illuminated and flying quite low over the border with Ukraine,” he told the paper.

Since Russia invaded Ukraine, there have been a number of intrusions into Polish airspace, triggering worry in the European Union member state and reminding people of how close the war is.

In 2022, two Poles were killed in a missile blast. Western officials blamed those deaths on a Ukrainian air defense missile that went astray but also accused Russia of culpability because it started the war, with the Ukrainian missiles launched in self-defense.

On Saturday night, one person was killed and four wounded in a Ukrainian missile attack on Sevastopol on the Russian-occupied Crimean peninsula, city governor Mikhail Razvozhaev said on his Telegram channel.