OSLO: Russia maintained gas flows through key pipeline routes into Europe on Monday, despite uncertainty over payment terms and as European leaders called for more sanctions against Moscow after war crimes allegations in Ukraine.

Physical gas flows through the Yamal-Europe pipeline, at Germany's Mallnow point see-sawed over the weekend and last stood at zero, data from operator Gascade showed.

Nominations, or requests, for Russian gas deliveries via Slovakia's Velke Kapusany entry point from Ukraine were steady on Monday at 967,841 MWh, as were flows through the Nord Stream 1 pipeline to Germany at 70,623,310 kWh/h.

Russian state-owned energy giant Gazprom said it was continuing to supply natural gas to Europe via Ukraine in line with requests from European consumers.

However, questions remain over future deliveries in light of the Kremlin's demand that buyers start paying Gazprom in roubles. Slovakia's Prime Minister Eduard Heger confirmed over the weekend that his country will act in unison with the European Union against such payment demands.

Calls for a new round of sanctions to hit Russia's economy also emerged over the weekend after reports of possible war crimes following the discovery of hundreds of bodies, some bound and shot at close range, around towns near Kyiv after Kremlin forces withdrew.

Germany's defence minister said on Sunday that the European Union must discuss banning the import of Russian gas in light of the reported atrocities, while French President Emmanuel Macron supported sanctions on oil and coal.

Lithuania has already announced it will no longer import Russian gas to meet its domestic needs, becoming the first country in Europe to secure its independence from Russian supplies.

Italian Ecology Transition minister Roberto Cingolani said the country has sufficient reserves to forego Russian gas supply over the next few months.

Italy and Germany are among the European Union members most dependent on Russian gas.

Russia has previously denied targeting civilians and has rejected allegations of war crimes. Moscow said the killings near Kyiv were "staged" to sully Russia's name.