Three people were injured in an explosion in the Kireevsky district of the Tula region on Sunday, Yekaterina Makarova, press secretary of the region's Ministry of Health, told Interfax.

Russian authorities and law enforcement agencies said a Ukrainian drone with ammunition caused the explosion in the town far from the two countries' border.

Kireevsk is about 180 miles from the border with Ukraine and 110 miles south of Moscow.

The Russian state-run news agency Tass reported authorities identified the drone as a Ukrainian Tu-141. The Latvia-based Russian news outlet Meduza reported that the blast left a crater about 50 feet in diameter and 16 feet deep.

-ABC News' Anastasia Bagaeva

Russia called Slovakia's transfer of MiG-29 fighter jets to Ukraine an unfriendly step and a step aimed at destroying bilateral relations.

"We are talking about another gross violation by the Slovak side of its international obligations to re-export Russian-made weapons and military equipment," Russia's Federal Service for Military-Technical Cooperation said in a statement.

"We regard these actions of Slovakia as an unfriendly act against the Russian Federation, aimed at destroying bilateral relations," the FSMTC said.

-ABC News' Will Gretsky

Ukrainian troops, on the defensive for four months, will launch a long-awaited counterassault "very soon" now that Russia's huge winter offensive is losing steam without taking Bakhmut, Ukraine's top ground forces commander Colonel-General Oleksandr Syrskyi said Thursday.

"The aggressor does not give up hope of taking Bakhmut at any cost, despite the losses in manpower and equipment," Syrskyi said.

Adding, "Without sparing anything, they lose considerable strength and exhale. Very soon we will take advantage of this opportunity, as we once did near Kyiv, Kharkiv, Balaklia and Kupyansk."

-ABC News' Will Gretsky

Slovakia has handed over four MiG-29 fighter jets to the Ukrainian Armed Forces, according to Slovakian Defense Minister Jaro Nad.

The remaining aircrafts promised to Ukraine will be handed over in the following weeks, Nad said.

In response to the news, Russia accused NATO and the EU of continuing to escalate the conflict in Ukraine and seeking to prolong it.

"The Russian Federation considers the transfer of four fighter jets by Slovakia to Ukraine a destructive step that runs counter to the EU's rhetoric about seeking peaceful solutions," Deputy Foreign Minister Alexander Grushko said in a statement.

Adding, "The Russian Federation will measure its reaction with the specific military activities of NATO on the territory of Finland."

-ABC News' Will Gretsky

A top Russian pro-war blogger has been killed in a bomb attack on a cafe in Russia, according to police.

The explosion on Sunday tore through a cafe in St. Petersburg, killing Vladlen Tatarsky, one of the best-known of the Russian military bloggers who have become influential during the war in Ukraine.

At least 30 other people were injured in the blast, according to the Ministry of Health. Video circulating online appeared to capture the aftermath, showing bloodied people emerging from the heavily damaged cafe.

The Russian Interior Ministry said an explosion has occurred in a cafe on the city's Universitetskaya Embankment.

"One person was killed in the incident, it was military correspondent Vladlen Tatarsky, the Russian Interior Ministry press center told reporters on Sunday.

Denis Pushilin, acting head of the Russian-backed Donetsk People’s Republic, issued a statement describing Tatarsky as "a great patriot" of the Donbass region of eastern Ukraine and Russia. Pushilin blamed the attack on the Kyiv regime, calling it a terrorist regime.

"A man with a difficult fate, Vladlen earned the respect of his comrades-in-arms because he lived and worked for the sake of truth and justice, for the sake of victory," Pushilin said of Tatarsky. "He managed to fight, and in the status of a military correspondent to make his contribution."

Pushilin said Tatarsky was to be awarded a medal "for the liberation of Mariupol" in eastern Ukraine.

It was the most serious bomb attack on a pro-war Russian figure inside Russia since the high-profile assassination of the Daria Dugina, the daughter of the ultra-nationalist Alexander Dugina, who was killed in a car bombing last year.

Tatarsky was a Russian ultra-nationalist and one of the best-known military bloggers, who strongly supported the war in Ukraine. He had also criticized the execution of the war by Russia’s military command.

Tatarsky had become a significant source of information for how the war was being fought on the Russian side.

His killing will likely set off speculation on whether Ukraine or Russia was behind his killing, similar to the Dugina episode.

In the Dugina case, U.S. intelligence sources eventually told The New York Times that Ukraine was behind the attack.

-News Patrick Reevell