At the same time as Russia attacks western Ukraine, Poland is moving its fighter jets

Eastern NATO countries are increasingly concerned about the risk of escalation of the war in Ukraine.

Poland once again challenged its defense with Russian attacks on western Ukraine near the Polish border.

The Polish armed forces announced on Friday that they had encountered fighter jets during these attacks and that no violation of the country's airspace had been recorded.

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It was the latest warning that Poland and other countries along NATO's eastern flank are deeply concerned about the risk of an escalation of the war in Ukraine as Russia appears to be accelerating its regional defense experiments. Later on Friday, Bulgaria's defense minister said Sofia had asked NATO for help to bolster its defenses.

During the overnight airstrikes across Ukraine, several strikes hit the Volyn region and 370,000 people lost power across the western region, which borders Poland. Governor Roman Romaniuk reported that two people were injured.

The governor of the region said that in the east of the city of Kharkiv, a drone attack killed three people and wounded five people. In central Ukraine, police said attacks on an apartment block in Oman injured a similar number.

Private power company DTEK announced on Friday that it had cut power across Kiev due to ongoing strikes.

In Russia, officials said: Air defense intercepted a Ukrainian drone attack on a heating plant in the Vladimir region.

Ukraine has had significant success in attacking Russia's energy infrastructure, especially its oil refineries. However, the strategy has drawn the ire of US President Donald Trump, who blames Ukraine for rising global oil prices.

Russia announced that it shot down 644 Ukrainian drones overnight, 94 of which were headed for Moscow.

In a report from Moscow, Al Jazeera reporter Yulia Shapovalova said that the capital's four airports and St. Petersburg's Pulkovo airport have suspended their operations.

Ukrainian strikes killed two people in the Russian-controlled Luhansk region of eastern Ukraine, the Russia-based governor said.

Concerns about Russian activity near NATO territory have grown since the summer as Romania, Moldova, Poland and the Baltic states reported multiple drones intruding into their airspace and waters.

It seems that this activity is becoming more hostile. In recent weeks, drones have targeted at least seven cargo ships in the territorial waters of Romania and Bulgaria in the Black Sea, killing two people and leaving at least 25 people still missing.

Drones attacked two ships off the coast of Romania this week. The collision of a merchant ship that sank off the coast of Bulgaria on Tuesday prompted Sofia to summon the Russian ambassador.

Bulgarian Prime Minister Roman Radev said on Friday that although the evidence points to Russia, his government does not have proof.

Shortly afterward, Defense Minister Dimitar Stoyanov told reporters that Bulgaria had formally asked NATO to deploy fighter jets and anti-drone systems to bolster its defenses.

"We have sent letters and a request to the NATO Secretary General and the Supreme Allied Commander asking them to strengthen their capabilities, which also means deploying additional forces on their soil," Stoyanov said. We are waiting for their decision."

Stoyanov said he plans to meet his Romanian and Turkish counterparts soon to discuss coordinated actions and a common approach to the situation in the Black Sea.

Bulgaria, which has proposed an end to attacks on civilian vessels in the Black Sea, also expects to join NATO's anti-drone initiative by the end of October.