Ukrainian President Volodymyr Zelensky on Monday accused Slovak Prime Minister Robert Fico of wanting to "help" President Vladimir Putin by continuing to import Russian gas.
Zelensky said EU leaders had observed that Fico, who visited Moscow on Sunday, opposes reducing energy dependence on Russia "implying that he wants to help Putin earn money to fund the war and weaken Europe".
"We believe that such assistance to Putin is immoral," he wrote on X.
Slovakia relies heavily on Russian gas and has raised concerns about the prospect of losing supplies as a contract for gas transit through Ukraine expires on December 31.
Ukraine has made it clear it will not renew the contract with Russia.
"This is a very difficult situation which requires increased attention," Kremlin spokesman Dmitry Peskov told reporters on Monday.
Fico is one of the few European leaders Putin has stayed friendly with Moscow since the 2022 eruption of hostilities with Ukraine.
The visit by Fico, whose country is a NATO and European Union member, had not been previously announced.
In a statement posted on his Facebook account after the talks, Fico said Sunday's meeting was "in response to" Zelensky opposing any "transit of gas through Ukraine to our territory".
Fico said Putin had confirmed Russia's "readiness... to continue to supply gas to the West and to Slovakia, which is practically impossible after 1 January 2025", but did not elaborate.
Both leaders also exchanged views on the conflict in Ukraine, and "the possibility of an early peaceful end" to it, he said.
