Poland's Senate speaker said Monday that Russia's authorities have denied him entry into the country for the funeral of slain Kremlin critic Boris Nemtsov.

Bogdan Borusewicz — Poland's leading opposition activist under communism — was to lead a delegation of Polish politicians and lawmakers attending Nemtsov's funeral Tuesday. Nemtsov was shot dead Friday night near the Kremlin.

Borusewicz told reporters he was informed he would not get a permission to enter Russia. It was not immediately clear if other members of the delegation would get their visas, but they were considering cancelling the trip.

The ban comes at a time when Poland's ties with Russia are strained over the conflict in eastern Ukraine.

Marcin Wojciechowski, spokesman for Poland's Foreign Ministry, said it was in response to European Union sanctions on the speaker of the upper house of the Russian parliament, Valentina Matviyenko.

A spokeswoman for the Russian Embassy, Valeria Perzhinskaya, confirmed that Borusewicz is on a list of western politicians who cannot enter Russia, but didn't elaborate.