KYIV, Ukraine (NewsNation Now) —  Leaders in Ukraine are calling on the world to “act immediately” as reports pour in of explosions in key cities after Russian President Vladimir Putin on Wednesday announced a military operation in the country.

“Whether at least something of the force of international law remains will depend on the world’s fair and just response to this aggression,” Ukrainian President Volodymyr Zelenskyy said.

Meanwhile, Ukraine’s Minister of Foreign Affairs Dmytro Kuleba posted on Twitter a list of five things he wants the world to do, saying “Future of Europe & the world is at stake.”

Here’s his demands:

• Devastating sanctions on Russia NOW, including SWIFT
• Fully isolate Russia by all means, in all formats
• Weapons, equipment for Ukraine
• Financial assistance
• Humanitarian assistance

U.S. response so far:

President Joe Biden said he would announce further sanctions targetig Russia on Thursday, in addition to financial measures imposed this week.

Biden said he spoke with Zelenskiy and briefed him on the steps Washington was taking to rally international condemnation of Russia, including at a special meeting of the United Nations Security Council.

“Tomorrow, I will be meeting with the leaders of the G7, and the United States and our allies and partners will be imposing severe sanctions on Russia,” Biden said in a statement.

Washington would continue to provide support and assistance to Ukraine and its people, he added, but gave no details.

Washington imposed the harshest measures Monday prohibiting trade and investment between U.S. individuals and the two breakaway Ukraine regions and moving Tuesday to cut off Russian state-owned Promsvyazbank and Vnesheconombank and 42 of their subsidiaries from the U.S. financial system.

The U.S. Treasury also barred trading in newly issued Russian sovereign debt, and ordered that assets relating to a handful of Russian elites and their family members be frozen.

Some financial industry executives have told the administration that they oppose any sanctions that would target Russia’s access to payment provider SWIFT, which is used by more than 11,000 financial institutions in more than 200 countries. 

Such a move could hurt Russian banks but it would also be disruptive for the global payments system and make it tough for creditors to get their money back from Russia.

While the White House has downplayed that option, lawmakers could pursue it. Although Congress is on recess this week, Isaac Boltansky, policy director for brokerage BTIG, said he expected lawmakers to advance legislation to challenge Russia’s action soon.

“There will also be an effort to ban Russia from the international payments infrastructure SWIFT, but there are concerns that doing so could harm Russian creditors awaiting funds,” he added.