Ukraine's President Volodymyr Zelenskyy will welcome United Nations Secretary-General Antonio Guterres for talks Thursday, as Ukraine pushes for an energy embargo and US Vice President Joe Biden drafts a plan for military, economic, and humanitarian assistance.

Guterres arrived in Ukraine with the stated goal of "expanding humanitarian assistance and ensuring the evacuation of civilians from conflict zones," which were among the themes discussed earlier this week in meetings with Russian President Vladimir Putin and Foreign Minister Sergey Lavrov.

"The sooner this war is over, the better – for Ukraine, Russia, and the rest of the world," Guterres tweeted.

The United Nations said Wednesday that it has teams in Moscow and Kyiv monitoring the implementation of Guterres' "in principle" agreement with Putin to allow the United Nations and the International Committee of the Red Cross to evacuate civilians trapped in the Azovstol steel plant in Mariupol's besieged port city.

"What we still have is a principled accord. We are attempting to transform that into a detailed understanding and a ground agreement," Guterres spokesman Farhan Haq told reporters. "Ultimately, we want to ensure that a cease-fire is observed, allowing us to move people safely."

"At the moment, we do not have those conditions," the official stated.

Energy from Russia

Mykhailo Podolyak, Ukraine's presidential adviser, said Thursday that an embargo on Russia's vital energy sector is "a matter of time."

While European nations have taken steps to reduce or eliminate their reliance on Russian oil and gas, the cost of replacing those supplies and the potential economic consequences at home has prompted some leaders to express caution about how quickly they should proceed down that path, even as Ukrainian officials called for an embargo.

Podolyak stated on Twitter that boycotting Russian energy supplies is a moral issue and a question of Russia ceasing to be a "reliable and predictable partner in the eyes of the world."

"While rapidly switching to alternative supply channels will be costly, it will be less costly than not doing so," Podolyak tweeted. "Moscow will suffer complete economic and political isolation in the medium term. As a result, Russia has never seen poverty on this scale."

His remarks come a day after Gazprom, Russia's state-owned gas company, cut natural gas shipments to Poland and Bulgaria.

Gazprom said Wednesday that Poland and Bulgaria had failed to comply with Russia's demand for payment in rubles for natural gas. According to Bloomberg News, the company said four unidentified natural gas importers paid Russia in rubles, while ten European companies opened ruble accounts to receive payments in the Russian currency.

The White House stated on Wednesday that Russia's move was anticipated.

"That is why we have been in contact with Europe, including these countries... over the last 24 hours, with the leaders of Poland and Bulgaria," White House press secretary Jen Psaki told reporters. "We have been working with partners around the world for months to diversify Europe's natural gas supply in anticipation of and to address near-term needs, as well as to replace volumes that would otherwise come from Russia."

Poland's President Andrzej Duda stated that the Russian gas shutdown breached "basic legal principles." In contrast, Bulgaria's Energy Minister Alexander Nikolov noted that gas was used as a "political and economic weapon."

Assistance from the United States

Biden is slated to deliver remarks Thursday "on support for Ukrainians defending their country and freedom against Russia's barbaric war," according to the White House.

Psaki told reporters Wednesday that Biden would send a suggested package to Congress this week that would be similar in scope to previous efforts to assist Ukraine, including security, humanitarian, and economic assistance to "address a range of the Ukrainians' needs."

The United States Congress might bring "lend-lease" legislation to Biden's desk for signature as early as this week, further liberalizing the flow of weaponry.

The US Department of Defense announced Wednesday that more than half of the country's 90 howitzers have arrived in Ukraine and that the first round of training on the long-range weaponry has concluded.

Pentagon spokesman John Kirby credited the continued flow of arms and assistance with Ukraine's continued victory in the fight against Putin's unjustified invasion.

"He is concentrating all of his firing forces in Ukraine's east and south. As a result, he has failed to accomplish any of his strategic objectives," Kirby stated. "I believe that is proof enough that the systems provided to Ukraine have had an effect on their self-defense requirements."