Sikorski, who also serves as a deputy prime minister, made the remarks in an interview with Italy's Corriere della Sera on Friday.
He was asked to comment on a statement by Dmitry Medvedev, deputy chairman of Russia's Security Council, who suggested that European companies cooperating with Ukraine's defence industry could become "targets".
The list reportedly includes four Italian and two Polish firms.
"Medvedev regularly threatens us with nuclear attacks, so this is actually a positive shift in his position," Sikorski said.
"We are so used to these threats that they no longer impress us much, but they must still be taken seriously."
Sikorski also recalled that Russia had sent 21 drones into Polish territory – a reference to an incident in September last year when Russian unmanned aircraft breached Polish airspace in an unprecedented violation.
On the battlefield situation, the minister said it was "clear that the Russians have lost momentum", but expressed concern that Putin's generals were withholding the truth from him.
He noted that Ukrainian strikes were affecting Russia's economy and its capacity to sustain the war.
Asked whether Putin is aware he has reached a dead end, Sikorski said: "Dictators always realise it too late. When you have held autocratic power for 20 years, there is no one around you willing to tell you the truth."
On US support, Sikorski said President Donald Trump's frustration that allies had not helped him in the conflict with Iran was not justified by either alliance commitments or NATO rules.
He also noted that American financial contributions to Ukraine had been "zero" since last year.
"Ukrainians also have their red lines. They want a peace that will last, not a temporary ceasefire," he said.
Sikorski added that he feared "for Putin, an unhappy war is better than a peace dangerous to Russia".
(ał)
Source: PAP