Radosław Sikorski made the statement in an interview with US broadcaster CNN on Monday night.
Poland's top diplomat said that Ukraine must be "given the tools" to repel the Russian invasion, adding Ukrainian defence forces had already destroyed "half of the Russian army."
He called on US lawmakers to greenlight the White House's new military support package for Kyiv.
Sikorski said Ukraine was under attack by an "aggressive dictator bent on recreating an empire," and stressed that the "consequences of Putin conquering Ukraine would be catastrophic."
"The cost of deterring Putin after he conquers Ukraine would be much much higher than the cost of keeping the Ukrainians supplied now,” the Polish foreign minister told CNN.
Tuesday is day 685 of Russia’s war on Ukraine.
Russia invaded Ukraine on February 24, 2022, launching the largest military campaign in Europe since World War II.
Source: CNN, PAP