While Russia launched massive missile strikes across Ukraine overnight, Ukrainian forces have claimed to have attacked a Russian military base on the occupied Crimean Peninsula.

A source in Ukraine's security services told ABC News on Thursday that Ukrainian forces had hit the Saki airfield in Moscow-annexed Crimea, using an initial wave of drones to "overload" Russian air defense. Russian air force assets were then struck using Neptune missiles designed and produced by Ukraine, according to the source.

Multiple unverified videos of the Ukrainian attack were circulating online Thursday.

-ABC News' Yulia Drozd, Oleksiy Pshemyskiy, Tatyana Rymarenko and Tom Soufi-Burridge

Russian forces launched missile strikes on at least five Ukrainian cities late Wednesday and early Thursday, just hours before Ukrainian President Volodymyr Zelenskyy's planned meeting with U.S. President Joe Biden in Washington, D.C.

Ukrainian Foreign Minister Dmytro Kuleba, who is traveling with Zelenskyy in the United States, described the strikes as "a massive missile attack" on civilian infrastructure, while Ukrainian state-owned grid operator Ukrenergo said it's the first major attack on the country's energy infrastructure in six months.

Russian forces fired a total of 43 missiles across Ukraine from east to west, and 36 of them were shot down by Ukrainian air defense, according to Gen. Valeriy Zaluzhny, commander-in-chief of the Ukrainian Armed Forces. The Ukrainian capital of Kyiv was among the major cities hit, along with areas of Kharkiv, Kherson, Cherkasy, Rivne and Lviv.

Ukrainian authorities were still assessing the damage and casualties on Thursday morning, but dozens of injuries have been reported so far. At least seven people were injured by falling debris in Kyiv.

Meanwhile, rescue efforts were ongoing in the central city of Cherkasy to evacuate as many as 20 people believed to be trapped beneath the rubble of a hotel that was destroyed in the strikes overnight. Thirteen others were already rescued and at least nine were injured, according to Ukrainian officials

The overnight strikes also targeted energy infrastructure in the Rivne region and an industrial zone in the Lviv area.

-ABC News' Victoria Beaulé, Guy Davies, Yulia Drozd and Tatyana Rymarenko.

Russian forces initiated six strikes on Kharkiv overnight, damaging civilian infrastructure, Ukrainian officials said early Thursday.

The mayor of Kyiv also said explosions occurred in the Ukrainian capital overnight. Debris from the downed rockets fell in the Darnytskyi and Holosiivskyi districts of the city.

Five people were hurt in the Darnytskyi district of Kyiv, where the strike also destroyed non-residential buildings. Three of them, including a 9-year-old girl, were hospitalized. Two were treated by medics on scene.

In the Shevchenkivskyi district of Kyiv, rocket debris damaged a gas pipe, an official said.

-ABC News' Will Gretsky

Seventeen people were killed, and 32 others injured, when a Russian missile hit a market in the center of Kostyantynivka in the Donetsk region, according to Ukrainian officials.

"At this moment, the artillery of Russian terrorists has killed 16 people in the city of Kostiantynivka, Donetsk region," President Volodymyr Zelenskyy said on Telegram. "A regular market. Shops. A pharmacy. People who did nothing wrong. Many wounded. Unfortunately, the number of casualties and the injured may rise."

Ukrainian President Volodymyr Zelenskyy arrived for his first NATO summit meeting in Lithuania's capital on Wednesday where he received a jovial welcome from world leaders eager to shake his hand -- a mood in keeping with the more conciliatory tone Zelenskyy has struck since landing in Vilnius.

The Ukrainian leader ultimately made a beeline for U.S. President Joe Biden, as NATO Secretary General Jens Stoltenberg created a path for him through the crowd of world leaders. The two men -- Biden in a suit and Zelenskyy in a dark green polo -- greeted each other with smiles and shook hands before chatting briefly.

Everyone eventually took their seats for the meeting of the NATO-Ukraine Council -- the first of its kind -- and Stoltenberg began his remarks with a warm welcome to Zelenskyy, whom he called "our dear friend."

"Welcome to this first meeting of the NATO-Ukraine Council," Stoltenberg said. "This is truly a historic moment, allies and Ukraine sitting side-by-side as equals to address our common vision of Euro-Atlantic security."

"And I'm really honored to welcome in our midst our dear friend, Volodymyr Zelenskyy, president of Ukraine. Welcome to Lithuania and it's great to have you here," he added.

Stoltenberg proceeded to give a very clear message about where NATO stands on Ukrainian membership, though no details on the pathway as has been a point of contention. He noted the summit has "reaffirmed that Ukraine will become a member of the alliance and we have made decisions to bring Ukraine closer to NATO."

"Today, we meet as equals," he said. "And I look forward to the day we meet as allies."

-ABC News' Cheyenne Haslett