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

Ukrainian President Volodymyr Zelenskyy spoke with Chinese President Xi Jinping in what was the two leaders' first official contact since January 2022, before Russia's invasion of Ukraine.

Xi announced that he will send a special envoy to visit Ukraine and "other countries" to work on a political solution.

"I believe that this call, as well as the appointment of Ukraine's ambassador to China, will give a powerful impetus to the development of our bilateral relations," Zelenskyy said in a statement on Twitter.

The Chinese government's official position still refuses to call the war an "invasion."

The call between the two leaders is said to have lasted an hour, according to Zelenskyy's office.

"Before the full-scale Russian invasion, China was Ukraine's number one trading partner. I believe that our conversation today will give a powerful impetus to the return, preservation and development of this dynamic at all levels," Zelenskyy said in a statement.

-ABC News' Karson Yiu, Cindy Smith and Will Gretsky