Radosław Sikorski was speaking at a joint press conference in Warsaw with Josep Borrell, the outgoing head of EU foreign policy, who visited Poland on Tuesday.

“There are developments at the frontline; there are developments in European capitals; there is the outcome of the U.S. election, which means that decision times are coming,” said Sikorski.

“Europe has a responsibility towards its citizens, towards its neighborhood, towards future generations, to do our utmost to get a fair deal [for Ukraine], to end the aggression, to establish the principles of international law, and to bring back the taboos that you may not change borders in Europe by force,” he added.

Finishing on a stark note, Sikorski warned: “If the rules cease to apply as a result of our actions or inaction, we have a dark future ahead of us.”

Taking his turn, Borrell praised Poland for the staunch backing it had provided Ukraine but underlined the need for other European countries to pull their weight given the uncertainty that has ensued following the U.S. election.

“There cannot be a situation where the Americans act and Europeans only react,” said Borrell. “We have to take responsibility ourselves—we must assure Ukraine that our support will continue, but this requires the appropriate resources and determination. This requires political will and, above all, financial resources.”

Borrell added that the situation will be discussed during next Monday’s meeting with the EU’s Foreign Affairs Council.