A Western ban on Russian oil imports may more than double the price to $300 a barrel and prompt the closure of the main gas pipeline to Germany, Moscow warned on Monday, as talks on Ukraine hardly advanced amid efforts to agree on civilian safe passage.

Russia’s invasion, the biggest attack on a European state since World War Two, has created 1.7 million refugees, a raft of sanctions on Moscow, and fears of wider conflict in the West unthought-of for decades.