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The European Union is proposing a ban on coal imports from Russia, opening the door for the first time to sanctions against Moscow's lucrative energy sector over the war in Ukraine.
Ursula von der Leyen, the president of the European Commission, will propose a coal embargo as part of a fifth package of sanctions which will need to be approved by the bloc's 27 members.
The package also includes a ban on some Russian shipping and on Russia importing certain high-tech items such as quantum computers and advanced semiconductors.
It comes after the grim discovery of corpses in Bucha, a town occupied and then abandoned by Russian forces, intensified pressure on the EU and other western countries to hit the Kremlin harder.
Julianne Smith, the US ambassador to Nato, said the world was "currently seeing the aftermath of war crimes and atrocities" and said Washington was working to collect evidence including first-hand accounts from Ukrainians.
"In the wake of the horrific images coming out of Bucha we feel even more compelled to take a fresh look at additional forms of assistance," she said.
Calls to cut off Europe's imports of Russian coal, oil and gas have previously run into concerns from some European countries, including Germany, that an embargo would make EU consumers pay rather than Russia.
Supporters of an embargo say Europe is essentially financing Russia's offensive in Ukraine by continuing to buy its fossil fuels, a process which the Kremlin says will eventually require payment in roubles.
Ukraine's Foreign Minister Dmytro Kuleba told reluctant nations on Tuesday that an import ban would stop "new Buchas" and said: "A few months of tightening your belts are worth thousands of saved lives."
Ms von der Leyen is proposing a potential compromise in which coal imports, worth about 4 billion euros ($4.4bn) a year, to be banned as a first step while oil and gas deliveries continue.
Although Russia provides about 45 per cent of the EU's hard coal imports, Europe is less reliant on such deliveries than it is on gas and oil shipments because it produces more coal and lignite within its own borders.
Ms von der Leyen said measures to stop oil imports were also being discussed along with further sanctions on individuals.
The energy-rich US has already stopped fossil fuel imports from Russia, while Britain plans to scrap oil imports this year and reduce what it says are already minimal gas deliveries. Coal deliveries are under review.
The EU's proposed shipping ban would stop Russian vessels from docking at the bloc's ports, but not if they are carrying energy, agricultural or food products or other essential goods.
Along with a proposed ban on Russian and Belarusian road haulage, it will add to restrictions in earlier rounds of sanctions which saw Russian planes banned from most of Europe's airspace.
Russia would also be banned from importing certain high-tech goods and from exporting wood, cement and seafood if the package is signed off by EU leaders.
"Clearly, in view of events, we need to increase our pressure further," Ms von der Leyen said. "Today, we are proposing to take our sanctions a step further. We will make them broader and sharper, so that they cut even deeper in the Russian economy."
Earlier rounds of western sanctions hit Russia's financial sector and prominent individuals in the Kremlin's inner circle, but critics say the fact that Moscow has not called off its invasion mean sanctions have not gone far enough.
The G7 countries - Britain, Germany, France, Italy, the US, Canada and Japan - are expected to hold talks this week on co-ordinating further sanctions amid outrage over the apparent massacre in Bucha.
The UK is urging the club of rich democracies to go after Russian gold and agree a timetable for phasing out all fossil fuel imports, Foreign Secretary Liz Truss said on Tuesday.
Nato foreign ministers will also hold talks in Brussels on Wednesday and Thursday to discuss further support for Ukraine, which Secretary General Jens Stoltenberg said might include additional anti-tank weapons.
However, the alliance is unwilling to intervene directly in Ukraine - even to establish a humanitarian zone, said Ms Smith, the US envoy to Nato, in a briefing ahead of that meeting.
She would not be drawn on reports in Czech media that the government in Prague had sent a shipment of T-72 Soviet-era battle tanks to Ukraine, which would go further than the exports of defensive weapons so far.
Mr Stoltenberg said Russia's withdrawal from around Kyiv, which led to the grisly discoveries in Bucha, appeared to herald a renewed attack on the south and east as it tries to secure a land bridge between the Donbas and occupied Crimea.
“This is a crucial phase of the war,” said Mr Stoltenberg, who said the Kremlin had "not given up its ambitions" in Ukraine despite the apparent failure of its assault on the capital.
Nato's 30 countries will be joined at the summit by Ukraine, Finland, Sweden and Georgia, and by Asia-Pacific partners Australia, Japan, New Zealand and South Korea.
Ms Smith said the US would look favourably on any Nato membership bid by Finland or Sweden, a possibility being debated in both countries.
