Poland’s prime minister, Donald Tusk, has said his government is working on a plan to prepare large-scale military training for every adult male in response to the changing security situation in Europe.

He said there was a need for an army of 500,000 soldiers, which would include reservists.

“We will try to have a model ready by the end of this year, so that every adult male in Poland is trained in the event of war, so that this reserve is really comparable and adequate to potential threats,” Tusk said in a major speech on security to the country’s Sejm, the lower house of parliament, on Friday.

Last year, the Polish government said the military encompassed about 200,000 soldiers and was to grow to 220,000 this year with the objective of increasing it to about 300,000.

But security fears have grown far more dramatic in recent weeks, as Russia continues to pound Ukraine with missiles and drones, and as the Trump administration has withdrawn military and intelligence support for Ukraine while putting its commitments to Nato in question.

“Today we are talking about the need for a half-million army in Poland,” Tusk said.

After his speech, he told reporters he was not considering a return of universal military service, but rather a reserve system based on the model in Switzerland. In that country, every man is obliged to serve in the military or an alternative civilian service while women can volunteer if they choose.

Tusk also suggested on Friday the country should explore nuclear “possibilities”. “We must be aware that Poland must reach for the most modern possibilities, also related to nuclear weapons and modern unconventional weapons,” he said.

And he backed withdrawing from a landmark treaty prohibiting the use of anti-personnel landmines, the Ottawa convention, as well as potentially from the Dublin convention, which bans the use of cluster munitions.

At least two other Nato countries, Finland and Lithuania – both also bordering Russia – have also in the past months mulled exiting the Ottawa convention.

“Let’s face it: it’s not something nice, nothing pleasant. We know that very well,” Tusk said. “The problem is that in our environment, those we may be afraid of, or those who are at war, they all have it.”

Poland, with a population of 38 million people, is located along Nato’s eastern flank and is deeply concerned by the war in Ukraine. There are fears that if Ukraine is defeated, Russia will turn its imperial ambitions next to countries like Poland, which Moscow controlled during the 19th century and during the cold war.

Jaroslaw Kaczyński, the head of Poland’s largest opposition party, the conservative Law and Justice, said a mental shift in society would also be needed in addition to the military training of men. “We will have a return to the chivalric ethos and to the fact that men should also be soldiers – that is, be able to expose themselves even to death,” Kaczyński said.

Concern has grown in Poland and across most of Europe as President Donald Trump has signalled the dramatic shifting of the US position to one that includes support for Russia’s position – even though on Friday he issued a stern warning to Russia after it attacked Ukrainian energy facilities with dozens of missiles and drones.

“If Ukraine loses the war or if it accepts the terms of peace, armistice or capitulation in such a way that weakens its sovereignty and makes it easier for [Russian president Vladimir] Putin to gain control over Ukraine, then, without a doubt – and we can all agree on that – Poland will find itself in a much more difficult geopolitical situation,” Tusk said.

Also on Friday, President Andrzej Duda said he was submitting an amendment to the Polish constitution for consideration which would oblige the country to spend at least 4% of its gross domestic product each year on defence.

Poland already spends a higher proportion of GDP on defence than any other Nato member, including the US. Last year Poland’s defence spending reached 4.1% of GDP, according to Nato estimates, and it plans to hit 4.7% this year.

But Duda said he wanted to take advantage of the consensus on the political scene in Poland today on the matter to enshrine it in the highest law.

Trump has suggested the US might abandon its commitments to the alliance if member countries don’t meet defence spending targets.

Associated Press, Reuters and Agence France-Presse contributed to this report