Russian officials have warned Ukrainians in occupied Kherson that they may be "deported" if they don't accept Russian passports, the U.K. Ministry of Defence said Monday.

"Russia is using passports as a tool in the 'Russification' of the occupied areas, as it did in Donetsk and Luhansk before the February 2022 invasion," the ministry on Twitter.

Residents of Kherson have been warned of penalties for those who don't accept Russian passports by June 1. Some may be removed from the territory or may have their property seized, according to the U.K.

Russia said Sunday that the U.S. has denied visas to Russian journalists who wanted to cover Foreign Minister Sergey Lavrov's trip to New York.

Lavrov promised that the decision will not be forgotten by their side.

"The country that calls itself the strongest, smartest, most free, fairest has chickened out, has done a silly thing and shown what its sworn assurances on protecting freedom of speech, access to information and so on are worth," he told reporters at the airport before his flight to New York.

"Most importantly, you can be sure: we will not forget, we will not forgive this," the minister told the pool of journalists who have not been granted U.S. visas.

The journalists had planned to cover Lavrov's appearance at the United Nations to mark Russia's chairmanship of the Security Council.

Russian Deputy Foreign Minister Sergei Ryabkov called the U.S.’s decision “outrageous” on Sunday, Interfax, a Russian news agency, reported.

There was no immediate comment from the U.S. State Department about the claim of refused visas, according to AP.

-ABC News’ Anastasia Bagaeva, Edward Szekeres, Natalia Shumskaia

Over 16,000 Ukrainian soldiers trained in the European Union, Josep Borrell, an EU representative for Foreign Affairs and Security Policy, said Friday.

The EU has delivered over $600 million of ammunition and missiles to Ukraine, according to Borrell.

-ABC News' Oleksiy Pshemyskiy

The Russian Defense Ministry reported that ammunition from a Russian Su-34 military aircraft fell in Belgorod, a city in the southern region of Russia.

"On the evening of April 20, during the flight of the Su-34 aircraft over the city of Belgorod, an abnormal descent of an aviation munition occurred," the agency said.

The ministry claimed buildings were damaged but there were no immediate reports of victims. An investigation is underway, according to the agency.

-ABC News' Will Gretsky

One year ago, with Ukraine's borders surrounded by what seemed to be a superior military force, many U.S. officials and analysts predicted a swift Russian blitz to Kyiv.

But after Russian President Vladimir Putin sent his more than 150,000 arrayed troops across the border, it soon became clear that a dual reassessment was in order: The Russian invaders were less potent than advertised, and the Ukrainians were unexpectedly stubborn and wily in the defense.

Some of the Russian troops weren’t even aware they were on a combat mission until Ukrainian bullets came cracking past them, according to U.S. officials. Meanwhile, Ukrainian forces stalled a massive Russian supply convoy through direct attacks and by destroying a key bridge. Only one week into the invasion, Putin's men were plagued with food and fuel shortages, morale running similarly low.

Kyiv stood.

"Putin assumed that Ukraine was an easy target, Putin assumed that Kyiv would easily fall, and Putin assumed that the world would stand by," U.S. Secretary of Defense Lloyd Austin said during a speech in Brussels last week. "But the Kremlin was wrong on every count."

Ukrainian forces were armed with more than grit.

They also had years of U.S. and NATO military training, plus American-made weapons, like anti-armor Javelins and anti-aircraft Stinger missiles. These made Russian vehicles vulnerable to ambush, and left Russian helicopter and jet pilots wary of flying over Ukrainian positions. Indeed, many airmen did not return from their sorties.

Despite astonishing losses of soldiers and vehicles, Putin has shown no inclination to end the conflict anytime soon. And despite its tenacity, Ukraine has also taken significant casualties, and is not able to produce enough of its own weapons and ammunition to keep up the fight.

Ukraine, after thwarting the advance on its capital, and later routing Russian forces from Kharkiv, now largely faces a battle of supply.

"When this war began, Russia had a larger population, a much bigger defense budget, a bigger military, bigger industrial base. So, this became an industrial war and a war of industrial bases," said Seth Jones, director of the International Security Program at the Center for Strategic and International Studies. "This is why Western industrial support has been so critical."

A key question now is, despite massive military aid packages and a promise to send even more, could the U.S. strategy ultimately result, not in a Ukrainian victory, but a stalemate in a years-long war of attrition?

-ABC News' Matt Seyler