In an interview with public broadcaster Polish Radio on Tuesday, Rau said that NATO officials had issued similar warnings.
Referring to Moscow's aggression against Georgia in 2008 and Ukraine in 2014, he added that "Russia’s policy towards its neighbors mostly boils down to the revision of borders."
“The message from Moscow was that the border revision process ... is not yet concluded,” Rau told Polish Radio, adding that Warsaw was seriously concerned over a "possible" new act of Russian aggression against Ukraine.
According to the Ukrainian intelligence service, Russia has amassed more than 90,000 soldiers at the Ukrainian border, and could be preparing for an attack at the end of January or beginning of February, public broadcaster Polish Radio’s IAR news agency reported.
US Secretary of State Antony Blinken said earlier this month that "a rehash" of the 2014 aggression against Ukraine would be "a serious mistake" for Russia.
In 2014, Russia annexed the Crimean Peninsula from Ukraine and fomented a separatist conflict in that country's eastern Donbas region, leading to a wave of EU and US sanctions against Moscow and Russian officials, Poland's PAP news agency has reported.