United Nations officials have been "blocked" from accessing "besieged cities like Mariupol, Mykolaiv and Kherson" — raising concerns of mass starvation in the Ukrainian cities that have been devastated by Russia's military invasion.

Driving the news: That's according to UN World Food Program chief David Beasley, who told CBS' "60 Minutes" journalist Scott Pelley in an interview broadcast Sunday that denying civilians in the eastern Ukrainian cities access to food was "just wrong, evil."

• Pelley asked Beasley during their interview in the Black Sea port city of Odessa how many people might be starving in Ukraine. "You've got to assume that millions are at stake right now," Beasley replied.
• "Why would you deny innocent victims of war food, non-combatants?" Beasley added.

State of play: The UN is running food assistance programs in cities including Odessa, which has also recently come under attack from Russian airstrikes.

• Beasley said they'd reached about 2 million people already. "We hope to scale up to 4 million in the weeks ahead and 6 million beyond that," he said. "It's going to be dependent upon two things: money and access."

Of note: Beasley said last month there's "no question" Russian forces were using food as a weapon of war in Ukraine.

Zoom out: During his interview with Pelley, Beasley noted that Ukraine was the "breadbasket of the world" with enough food to feed 400 million people, so Russia's military assault was "creating havoc for the poorest of the poor around the world," but it would also "affect everybody."

• "You're already seeing fuel pricing spike, food pricing spike, cost of shipping spiking," he said.

The big picture: UN Secretary-General António Guterres last month visited Ukraine and Russia in an effort to help civilians fleeing the war and those trapped in besieged Ukrainian cities with limited access to running water, electricity and food.

• Russian President Vladimir Putin focused on defending his forces' invasion during his Moscow meeting with Guterres.
• The Kremlin has repeatedly denied that its forces have committed atrocities including the targeting of civilians, as the International Criminal Court and others investigate whether human rights violations such as war crimes have been committed in Ukraine.

Between the lines: War crimes have been historically hard to investigate, and often they're even more challenging to prosecute, Axios' Laurin-Whitney Gottbrath writes.

Food shortages "another catastrophic effect" of Russia's war, USAID chief warns