Poland has scrambled fighter jets just hours after a top general warned Russia is preparing for war against NATO. The Eastern European country’s armed forces posted on social media details of “preventative” actions taken overnight to secure airspace in parts of Poland close to regions in Ukraine under attack from Russia.

It said “necessary” forces and resources were activated, including fighter jets and an early warning aircraft. Radio detection, reconnaissance systems and ground-based air defences have also been placed on “maximum readiness”, according to a translation of the tweet.

Poland’s armed forces added: “These actions are of a preventive nature and are aimed at securing the airspace and its protection, especially in areas adjacent to the threatened regions.”

The announcement comes after Chief of the General Staff of the Polish armed forces, Wieslaw Kukula, warned that Russia has “begun the period of preparing for war”.

He claimed Moscow is “building an environment” in Poland aimed at creating “favourable” conditions for potential aggression on Polish territory.

An attack on Poland would trigger a response from NATO under Article 5 the military alliance’s treaty which states an armed attack on one member is an attack on all.

Russia’s huge overnight attacks on Ukraine saw power cuts in cities in the west of the country. A large blaze hit Lviv, according to The Kyiv Independent newspaper, citing Lviv City Council deputy Ihor Zinkevich.

Lviv’s Mayor Andrii Sadovyi said a warehouse storing tyres was hit, but there were no casualties.

Authorities reported “hits on residential buildings” in the city of Ternopil, according to the same publication. Dmytro Lubinets, the Ukrainian Parliament Commissioner for Human Rights, said at least nine people were killed and dozens were injured when a block of flats in Ternopil was hit.

Tensions have escalated further in Poland over recent days, following the explosion of a railway line at the weekend.

Polish Prime Minister Donald Tusk said on Tuesday that the suspects were two Ukrainians believed to be working for Russia.

Mr Tusk has described the explosion on a line linking Poland’s capital, Warsaw, to the border with Ukraine as an “unprecedented act of sabotage”.

In a separate incident, which Polish officials have confirmed as sabotage, power lines over another stretch of the same rail line further south were also damaged.

When asked to comment on Polish statements saying that two Ukrainian nationals working for Russia had sabotaged a railway line, Russia’s presidential spokesperson Dmitry Peskov said it would be “strange if Russia wasn’t blamed first”.