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

At least six civilians were killed and eight others were injured Sunday when Russian missiles slammed into houses and apartment buildings in an eastern Ukrainian city, Ukrainian officials said.

The attack occurred in downtown Kostiantynivka, a city in the Donetsk region of eastern Ukraine, the site of the war’s fiercest fighting.

Andriy Yermak, deputy head of the Ukrainian Presidential Office, said at least six people were killed in the attack.

Three Russian S-300 long-range missiles and four other rockets hit homes and apartment buildings in Kostiantynivka, according to Pavlo Kyrylenko, the regional governor.

Kostiantynivka is about eight miles west of the embattled town of Bakhmut, currently the main hotspot of the war.

-ABC News' Tatiana Rymarenko