Russia's "special military operation" in Ukraine will continue "until the objectives are achieved," Russian Defense Minister Sergei Shoigu said Tuesday.

Shoigu claimed that Russian troops are "actively providing humanitarian assistance to the population of" the self-declared Donetsk and Luhansk people's republics as well as Ukraine.

"As many as 684 humanitarian operations have been completed and 6,079 tons of cargo have been supplied to 210 populated localities," Shoigu said at a teleconference.

Russian forces struck Mykolaiv's regional state administration building on Tuesday morning, Ukrainian authorities said.

A video posted on Telegram by Mykolaiv Oblast Gov. Vitaliy Kim and verified by ABC News shows the moment the building was hit. A live webcam over the southern city of Mykolaiv captured the missile crossing the camera. Moments later, smoke from an explosion fills the screen.

Another video posted on Facebook by the State Emergency Service of Ukraine and verified by ABC News shows a gaping hole in the building where the missile hit. At least seven people were killed and 22 others were injured. Search and rescue operations are ongoing, according to the State Emergency Service.

An image posted on Twitter by Ukraine's Center for Strategic Communication and Information Security (Stratcom) also showed the destroyed building.

-ABC News' Monica Camacho and Fergal Gallagher

French President Emmanuel Macron will speak via telephone with his Russian counterpart Vladimir Putin on Tuesday, according to the Elysee Palace.

Their phone conversation is scheduled for 4:30 p.m. Paris time.

-ABC News' Ibtissem Guenfoud

Russian billionaire Roman Abramovich is taking part in Russian-Ukrainian negotiations at the approval of both parties, although he is not an official member of the Russian delegation, according to Kremlin spokesman Dmitry Peskov.

"Abramovich has been engaged in ensuring certain contacts between the Russian and the Ukrainian side," Peskov said during a daily call with reporters Tuesday. "He is not an official delegation member."

"Nevertheless, he is also present on our side in Istanbul," Peskov added, referring to the peace talks currently underway in Turkey's capital.

Abramovich's participation in the negotiations has been endorsed by both sides, according to Peskov.

Peskov said it will be clear "today or tomorrow whether [the talks] hold some promise or not."

All Russian troops have left the Ukrainian cities of Kyiv and Chernihiv, withdrawing north toward the borders of Belarus and Russia to consolidate before likely redeploying to the Donbas region in eastern Ukraine, a senior U.S. defense official told reporters Wednesday.

But even with the Russians gone, the territory remains treacherous.

"There are some indications that they left behind mines and things like that, so the Ukrainians are being somewhat careful in some areas north of Kyiv as they begin to clear the ground and clear the territory and re-occupy it," the official said.

While the U.S. hasn't yet seen these troops redeploy elsewhere in Ukraine, it'll likely happen soon, according to the official. Ukrainian forces are preparing for a major fight in Donbas, the official said.

The official also said the Pentagon is "monitoring" an apparent nitric acid explosion in Ukraine's Luhansk region, which Russia blamed on Ukraine.

"We've seen the Russians claim that this was a Ukrainian attack on this. We do not believe that is true," the official said. "We do believe that the Russians are responsible, but exactly what they used when they did it, why they did it, what the damage is, we just don't have that level of detail," the official said.

The official also noted that a small number of Ukrainians currently in the U.S. for "professional military education" were pulled aside for a couple days of training on Switchblade drones, which the U.S. is sending overseas as part of its military aid, according to the official.

"Although it's not a very difficult system to operate, we took advantage of having them in the country to give them some rudimentary training on that," the official said.

-ABC News' Matt Seyler