Russian President Vladimir Putin held surprise talks with Slovak Prime Minister Robert Fico at the Kremlin on Sunday to discuss the future of Russian gas deliveries.
The two leaders also discussed the conflict in Ukraine, just hours after Putin had warned of harsh reprisals against Kyiv over a drone attack.
Slovakia, which heavily relies on Russian gas, has raised concerns about the prospect of losing supplies as a contract allowing its transit through Ukraine expires by year-end. Ukraine has made it clear it will not renew a transit contract that expires on December 31.
Fico is one of the few European leaders Putin has stayed friendly with 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.
Russian TV journalist Pavel Zarubin, a Kremlin insider, posted a short video showing the two leaders smiling and shaking hands.
Later Sunday, Kremlin spokesman Dmitri Peskov only confirmed that the meeting had ended, adding that the two leaders would not make a joint statement.
But Fico, in a statement posted on his Facebook account after the talks, said Sunday's meeting was "in response to" Ukrainian President Volodymyr 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 exchanged views on the conflict in Ukraine, and "the possibility of an early peaceful end" to it.
- Putin vows 'destruction' -
Fico blamed Kyiv for being "in favour of sanctions" against Russia's nuclear programme. He said that was "harming Slovakia financially and threatening the production of electricity in nuclear power plants" in the country.
Fico ended military aid to Ukraine when he became prime minister again in October 2023. Like Hungarian counterpart Viktor Orban, he has called for peace talks.
He also announced in November that he would go to Moscow in May for ceremonies to mark the 80th anniversary of the end of World War II.
Earlier Sunday, Putin vowed to bring more "destruction" to Ukraine after a drone attack on Kazan on Saturday.
Videos on Russian social media showed drones hitting a high-rise glass tower block and setting off fireballs, though there were no reported casualties.
Ukraine has not commented on the strike.
But Putin told a televised government meeting: "Whoever, and however much they try to destroy, they will face many times more destruction themselves and will regret what they are trying to do in our country."
The Kazan strike was the latest in a series of escalating aerial attacks in the nearly three-year conflict.
Putin has previously threatened to target central Kyiv with a hypersonic missile in response to Ukrainian attacks on Russian territory.
And Russia's defence ministry has described strikes on Ukrainian energy facilities over recent weeks retaliation for Kyiv using Western-supplied missiles to hit Russian air bases and arms factories.
- Russia claims fresh advances -
The threats heightened as Russia claimed fresh battlefield advances in east Ukraine.
The defence ministry said on Telegram that troops had "liberated" the villages of Lozova in the northeastern Kharkiv region and Krasnoye -- called Sontsivka in Ukraine.
Krasnoye is close to the resource hub of Kurakhove, which Russia has almost encircled and would be a key step in its efforts to capture the entire Donetsk region.
Russia has in recent months sought to secure as much territory as possible before US President-elect Donald Trump comes to power in January.
The Republican has promised to end the conflict, without specifying how.
Moscow's army claims to have seized more than 190 Ukrainian settlements this year, as the rival army struggles with manpower and ammunition shortages.
Ukraine on Sunday also accused Russian forces of killing captured soldiers -- an alleged war crimes violation.
A video posted by Ukraine's 110th separate mechanised brigade showed "the shooting of soldiers who surrendered," Kyiv's human rights ombudsman Dmytro Lubinets said in a post on Telegram.
Drone footage showed Russians shooting the Ukrainians at point-blank range after they had already surrendered, he said.
AFP could not verify the footage.
Ukraine has made several allegations of war crimes during the conflict.