Russia's war against Ukraine could create a refugee crisis of up to 4 million people in the coming days and weeks, a U.N. commissioner told the Security Council on Monday afternoon.

"I have rarely seen such an incredibly fast rising exodus of people -- the largest, surely, within Europe since the Balkan wars," United Nations High Commissioner for Refugees Filippo Grandi told the New York-based council via video teleconference from Geneva.

At least 520,000 refugees have already fled Ukraine, but Grandi said the number is "rising exponentially, hour after hour." That includes 280,000 to Poland, 94,000 to Hungary, 40,000 to Moldova, 34,000 to Romania, 30,000 to Slovakia, tens of thousands in other countries, and a "sizable number" to Russia.

In Ukraine itself, Grandi said the U.N. is "not even scratching the surface of meeting the needs of Ukrainians."

"The situation is moving so quickly, and the levels of risk are so high by now, that it is impossible for humanitarians to distribute the help that Ukrainians desperately need," he said.

Monday's U.N. Security Council session was meant to more narrowly focus on the humanitarian crisis, as opposed to the war itself. U.N. aid chief Martin Griffiths announced the U.N. will make an urgent humanitarian appeal by Secretary-General Antonio Guterres on Tuesday -- a three-month flash appeal for the crisis in Ukraine and a longer-term appeal for the refugee crisis in the region.

-ABC News’ Conor Finnegan

The European Council extended sanctions against Russia to include 26 more individuals and an additional entity, the Council said in a statement Monday.

The new listings include oligarchs and businessmen active in the oil, banking and finance sectors as well as government members, high-level military personalities and propagandists who contributed to the spread of anti-Ukrainian propaganda and promoted a positive attitude toward the invasion of Ukraine.

Some prominent individuals on the list include Igor Sechin, CEO of Rosneft, a Russian state oil company; Nikolay Tokarev, CEO of Transeft, a major Russian oil and gas company; Alisher Usmanov, a pro-Kremlin oligarch with close ties to Russian President Vladimir Putin; and Petr Aven, one of Putin's closest oligarchs.

The EU’s restrictive measures now apply to a total of 680 individuals and 53 entities.

-ABC News' Christine Theodorou

The White House is not ruling out imposing restrictions on importing Russian oil and gas, White House press secretary Jen Psaki said in a briefing Monday afternoon.

"We haven't ruled out that," she said.

The sanctions announced this past week by the Biden administration did not directly hit oil and gas flows from Russia, which would deal a major blow to the energy market as the global economy continues to recover.

The White House has raised concerns about already high energy costs for Americans going even higher if this trigger is pulled.

Remaining "on the table" as well is the option to tap into the strategic petroleum reserve, though Psaki didn't have updates on that decision.

"There are conversations that we've been having with global partners, and obviously we have our own strategic petroleum reserve stockpile to tap into," she said.

When asked about Canadian Prime Minister Justin Trudeau's announcement that Canada would unilaterally ban Russian crude oil imports and whether the U.S. would make a similar move without coordination from European partners, Psaki repeated that "all options remain on the table."

"You have seen us take a number of actions over the last several days that play that out," she said. "But I don't have anything to predict at this point other than to reiterate that we have really worked to take steps in lockstep with the Europeans and a number of our NATO partners."

Psaki said the White House also continues to be in touch with Saudi Arabia to try and minimize the impact on energy markets across the world as the Russian invasion of Ukraine continues.

She would not say if the U.S. made any request to Saudi Arabia or OPEC+ members to increase production given the ongoing crisis.

"There is an ongoing discussion about steps that we can take to address volatility in the market," Psaki said.

-ABC News' Justin Gomez

The International Criminal Court is "opening an investigation into the situation in Ukraine, as rapidly as possible," the court's chief prosecutor, Karim A.A. Khan, announced Monday.

The court has "reasonable basis to believe" that war crimes and crimes against humanity were committed in Ukraine and is pursuing accountability, including possible prosecutions, Khan said in a statement.

An authorization from a pretrial chamber of the court and support and funding from the ICC's 123 member states will be required to begin an investigation.

Neither Russia nor Ukraine is a member of the court, but Ukraine has provided authorization for an investigation in its territory, Khan said.

The U.N. Human Rights Council also voted Monday to hold an urgent debate on Thursday, where they'll consider a draft resolution from Ukraine.

-ABC News' Conor Finnegan