Polish Prime Minister Donald Tusk has warned of the "real" threat of conflict in Europe, saying that for the first time since the end of World War II, the continent has entered a "pre-war era".

"War is no longer a concept from the past. It is real, and it started over two years ago. The most worrying thing at the moment is that literally any scenario is possible. We haven't seen a situation like this since 1945," Tusk said in an interview for the European media grouping LENA on Friday.

"I know it sounds devastating, especially for the younger generation, but we have to get used to the fact that a new era has begun: the pre-war era. I'm not exaggerating; it's becoming clearer every day."

Former European Council president Tusk, whose country has been one of the staunchest supporters of neighboring Ukraine, said Friday that if Kiev lost its war with Russia, "no one" in Europe would feel safe.

The Polish premier urged immediate aid for Kiev, emphasizing that the outcome of the next two years of the conflict would be pivotal.

His remarks came closely after the Polish military claimed Sunday that a Russian air-launched cruise missile entered the country's airspace for around 40 seconds near the southeastern village of Oserdow, prompting Warsaw to elevate its military preparedness.

Touching on the upcoming US presidential election in November, Tusk indicated that irrespective of the results this year, Europe would emerge as a more appealing ally for Washington provided it enhances its military self-reliance.

"Our job is to nurture transatlantic relations, regardless of who the US president is," Tusk said in the interview.