Missiles hit a number of Ukrainian cities, killing at least 30 people in one of the deadliest attacks in months.

"Due to the new aggressive activity by Russians in Ukraine, all necessary procedures have been initiated to ensure the safety of Polish airspace. Increased noise levels may occur in the southeastern part of the country due to actions in our airspace by Polish and allied military aviation," the Operational Command of the Armed Forces said on Monday.

The statement added that the Polish Armed Forces were monitoring the situation and were ready to react to any threats.

The Operational Command later issued a statement saying that the situation had calmed, but anxiety persists over the dangers posed to Poland by Russian military activity.