The fatal shooting in eastern Poland of a Russian artist known for his caricatures of Russian President Vladimir Putin was likely politically motivated, Polish Prime Minister Donald Tusk said on Wednesday.

“All indications are that this is a political murder,” Tusk said of the killing of Semyon Skrepetsky, whose real name is Robert Kuzovkov. “If it was commissioned by Russia, then this is also a very serious matter with an international dimension.”

According to Polish officials, Skrepetsky was shot three times on Monday morning by an unidentified gunman armed with a handgun. When the artist fell to the ground, he was approached by the assailant, who fired two more shots at close range.

The Polish government says it offered Skrepetsky protection, which he declined.

Two Belarusian citizens were arrested in conjunction with the artist’s death, but they have since been released, according to Polish officials. An investigation by Polish services is ongoing.

The case risks rekindling tensions between Poland and its neighbour Russia, exacerbated by drone crashes on Polish territory last autumn, which Warsaw blames on Moscow.

Skrepetsky was known for his sometimes provocative caricatures, which targeted prominent Russian political figures – ranging from Putin and Soviet leader Joseph Stalin to opposition figure Alexei Navalny and Chechen ruler Ramzan Kadyrov.