Ukraine Hosts UN Chief Guterres, Urges Russian Oil EmbargoUkrainian President Volodymyr Zelenskyy is hosting U.N. Secretary-General Antonio Guterres for talks Thursday, while Ukraine calls for an embargo on Russian energy supplies and U.S. President Joe Biden prepares a proposal for military, economic and humanitarian aid. Guterres toured areas outside Kyiv, including Bucha, where the bodies of civilians were found after Russian forces withdrew from the area. Those discoveries prompted calls for investigations of possible war crimes, and Guterres on Thursday encouraged Russia to cooperate with probes by the International Criminal Court. "I fully support the ICC and I appeal to the Russian Federation to accept, to cooperate with the ICC,” Guterres said. “But when we talk about war crimes, we cannot forget that the worst of crimes is war itself.” The U.N. chief said after arriving in Ukraine that he wanted to “expand humanitarian support and secure the evacuation of civilians from conflict zones,” topics that were part of his talks earlier this week with Russian President Vladimir Putin and Foreign Minister Sergey Lavrov. “The sooner this war ends, the better — for the sake of Ukraine, Russia, and the world,” Guterres tweeted. Russian energy Ukrainian presidential adviser Mykhailo Podolyak said Thursday “it’s a matter of time” before an embargo is imposed on Russia’s key energy industry. While European nations have taken steps to reduce or eliminate their reliance on Russian oil and gas, replacing those supplies and potential economic hits at home have made some leaders express caution about how quickly to proceed down that path as Ukrainian officials called for an embargo. Podolyak tweeted that avoiding Russian energy supplies is both a moral issue and a matter of Russia ceasing “to be a reliable and predictable partner in the eyes of the world.” “Switching to alternative supply channels quickly will be expensive, but not as expensive as not doing so,” Podolyak tweeted. “In the medium term, Moscow will face total economic and political isolation. As a result, poverty, the scale of which Russia has not seen yet.” SEE ALSO: His comments came a day after Russia’s Gazprom halted natural gas supplies to Poland and Bulgaria. Gazprom said Wednesday that Poland and Bulgaria had not met Russia’s demand to pay for natural gas in rubles. The company said four unnamed natural gas buyers have paid Russia in rubles, and 10 European companies have created ruble accounts to make payments in the Russian currency, Bloomberg News reported. The White House said Wednesday this move by Russia was anticipated. “That is why we, of course, had been in touch with Europe, including with these countries ... over the last 24 hours, with leaders in Poland and Bulgaria,” White House press secretary Jen Psaki told reporters. “We have been working for some time now, for months with partners around the world to diversify natural gas supply to Europe in anticipation of, and to also address, near-term needs and replace volumes that would otherwise come from Russia.” Polish President Andrzej Duda said the Russian gas cutoff violated "basic legal principles," while Bulgarian Energy Minister Alexander Nikolov said gas was being used as a "political and economic weapon." U.S. aid The White House said Biden is scheduled to deliver remarks Thursday “on support for Ukrainians defending their country and their freedom against Russia’s brutal war.” Psaki told reporters Wednesday that Biden would send to Congress this week a proposed package similar in focus to those already carried out to help Ukraine, with security, humanitarian and economic assistance to “help address a range of the needs the Ukrainians have.” The U.S. Congress could also send “lend-lease” legislation further freeing up the flow of weapons to Biden’s desk for a signature as early as the end of this week. The U.S. Department of Defense said Wednesday more than half of the 90 U.S. howitzers have reached Ukraine, and a first round of training on the long-range weapons has already wrapped up. Pentagon press secretary John Kirby cited the ongoing flow of weapons and aid in the success Ukraine has maintained in the battle against Putin’s unprovoked invasion. “He's concentrating all his firing forces in the east and in the south of Ukraine. So, he has achieved none of his strategic objectives,” Kirby said. “I think that's proof right there that the kinds of systems that are being provided to Ukraine have had an effect ... on their self-defense needs.” Russian President Vladimir Putin warned against Western intervention in Ukraine as he spoke to lawmakers in St. Petersburg on Wednesday. "If someone intends to intervene in the ongoing events from the outside, and create strategic threats for Russia that are unacceptable to us, they should know that our retaliatory strikes will be lightning-fast," Putin said. "We have all the tools for this, things no one else can boast of having now. And we will not boast, we will use them if necessary. And I want everyone to know that." Support reaches $8 billion Military support for Ukraine, either pledged or provided already by NATO allies, has reached $8 billion, NATO Secretary General Jens Stoltenberg said Thursday. Russia’s invasion of Ukraine has pushed Finland and Sweden to consider applying to be members of the NATO military alliance, and Stoltenberg said if they do choose to take that step, the process could be completed quickly. "It is, of course, for Finland and Sweden to decide whether they would like to apply for membership in NATO or not. But if they decide to apply, Finland and Sweden would be welcomed with open arms to NATO,” Stoltenberg told reporters in Brussels. Russia has expressed opposition to prospective NATO membership for Finland and Sweden, saying if they do join, Russia will deploy nuclear weapons and hypersonic missiles to Kaliningrad. "This is fundamentally about the right of every nation in Europe to decide its own future,” Stoltenberg said. “So when Russia tries to threaten, to intimidate Finland and Sweden from not applying, it just demonstrates how Russia is not respecting the basic right of every nation to choose its own path." National security correspondent Jeff Seldin contributed to this report. Some information came from The Associated Press, Reuters and Agence France-Presse.