Smoke was spotted coming from the Russian embassy in the Polish capital Warsaw, the niezalezna.pl website reported on Wednesday, citing the Open Source Intelligence Monitor.
"There are claims that Russian diplomats are burning documents,” niezalezna.pl said.
It added that the same happened at the Russian embassy in the Ukrainian capital Kyiv right before Moscow's invasion of the country.
According to the Open Source Intelligence Monitor, "this does not mean that Russia is preparing to invade Poland but it may be a sign that Russian diplomats may be preparing to leave the country for some reason.”
The report comes as Poland "openly supports Ukraine where innocent people are being killed every day, as the country is being systematically destroyed" by Russian troops, niezalezna.pl said.
Poland on Wednesday said it was expelling 45 Russian diplomats suspected of being intelligence operatives.
Wednesday is day 28 of the Russian invasion of Ukraine.
Poland on Wednesday reported it had welcomed nearly 2.18 million refugees fleeing Russia's attack on Ukraine.