Zbigniew Rau made the statement during a visit to Iran, Polish state news agency PAP reported.
He added that the incident “should not have taken place” as “diplomats enjoy special protection regardless of the policies of their governments.”
The Polish foreign ministry issued a statement to say that the "event which occurred today while the Ambassador of the Russian Federation was about to lay a wreath at the Soviet Military Cemetery was a regrettable incident which should not have taken place."
It reiterated in its statement that "diplomats enjoy particular protection, irrespectively of policies pursued by their governments."
Earlier, the Polish foreign ministry said it was "aware of the gravity of the situation” and was "monitoring developments.”
It added that "so far there has been no decision" to recall the Polish ambassador from Moscow, the rmf24.pl website reported.
Russia’s ambassador to Poland, Sergiy Andreev, was doused in red liquid by anti-war campaigners as he attempted to lay flowers at the Soviet Military Cemetery in Warsaw on Monday.
He was there to mark Victory Day, when his country celebrates defeating Nazi Germany in World War II.
After the pro-Ukraine protesters sprayed red paint on him, Andreev returned to his car, telling reporters he was “proud” of his country and President Vladimir Putin.
He was later quoted by Russian media as saying he did not suffer any injuries and did not notify the police, but would “submit a note of protest” to the Polish government over "failure to maintain public order."
“The emotions of Ukrainian women are understandable’
Meanwhile, Poland’s Interior Minister Mariusz Kamiński said on Twitter: “The rally against the Russian aggression on Ukraine, where the crime of genocide is being perpetrated every day, was legal.”
He added: “The emotions of the Ukrainian women taking part in the protest, whose husbands are fighting bravely in defence of their homeland, are understandable.”
Kamiński also said that Polish authorities “did not recommend” that Andreev lay the flowers at the cemetery on May 9, and that police enabled him “to safely drive away from the scene.”
Russia's May 9 event in Warsaw cancelled
At the weekend, the Russian embassy announced it was cancelling its traditional May 9 event, after Warsaw Mayor Rafał Trzaskowski said there would be “no consent from me to the aggressor’s celebration in Warsaw.”
The Polish foreign ministry also refused to support the memorial event amid Russia’s invasion of Ukraine, reporters were told.
Nevertheless, Andreev decided to proceed with his plan of laying wreaths at the Soviet cemetery.
The 19-hectare Soviet Military Cemetery in Warsaw holds the remains of more than 20,000 troops who lost their lives between 1944 and 1945, according to the PAP news agency.
Monday was day 75 of Russia’s war on Ukraine.
Source: PAP, gov.pl