A rocket strike on a regional administration building in the southern Ukrainian port city of Mykolaiv killed 12 and injured 33 people, according to Ukrainian State Emergency Services.

Emergency services said 18 people were rescued from the rubble.

According to state officials, the strike occurred Tuesday at 8:45 a.m. local time. Search and rescue operations are still underway.

-ABC News' Natalya Kushnir

Gen. Tod Wolters, the top U.S. military commander in Europe, met with lawmakers on Capitol Hill Tuesday, telling them he expects he’ll need more U.S. troops and it’s possible they may become a permanent force in the country.

With U.S. troop levels in Europe now at 100,000 from 60,000 just a few months ago, Wolters said it’s very likely that the number of troops could continue to rise depending on the situation in Ukraine.

“My suspicion is we're going to still need more,” Wolters said. "And obviously, there's always a mix between the requirement of permanent versus rotational and there are pluses and minuses of each one. We'll have to continue to examine the European contributions to make a smart decision about where to go in the future."

Wolters praised Ukraine’s military and its ability to stall Russian military operations through the weapons systems provided by the U.S. military.

When asked if the U.S. had overestimated the Russians and underestimated Ukraine’s defensive capability, Wolters said in part, "When this crisis is over with we will accomplish a comprehensive after-action review in all domains and in all departments and find out where our weak areas. Where it makes sure that we can find ways to improve and this could be one of those areas."

-ABC News' Luis Martinez

The United Kingdom's National Crime Agency said it's seized a superyacht owned by a Russian national -- worth around $49.92 million -- in Canary Wharf in London.

The National Crime Agency's statement doesn't identify the Russian national but says the owner deliberately registered the ship to a company based in Saint Kitts and Nevis in the Caribbean. The agency also said the ship carried Maltese flags, allegedly to hide its origins.

British Transport Secretary Grant Shapps said the seizure "turned an icon of Russia’s power and wealth into a clear and stark warning to Putin and his cronies." Shapps said the seizure proves "we can and will take the strongest possible action against those seeking to benefit from Russian connections."

-ABC News' Christine Theodorou

Belgium announced Tuesday its decision to expel 21 Russian intelligence officers.

The officers were working for the Russian embassy and consulate in Brussels and were allegedly involved "in espionage and influence operations threatening national security," Belgian Foreign Minister Sophie Wilmes said in a statement on Twitter.

Meanwhile, the Netherlands said it has expelled 17 Russian intelligence officers. The officers were in The Netherlands under diplomatic cover, Dutch Foreign Minister Wopke Hoekstra said in a statement on Twitter.

Ireland confirmed it has asked four senior Russian officials to leave the country.

"This is because their activities have not been in accordance with international standards of diplomatic behaviour," Irish Foreign Minister Simon Coveney said in a statement posted to Twitter. "The Government continues to believe that diplomatic channels between Ireland and the Russian Federation should remain open."

The Czech Republic also announced its decision to expel one Russian diplomat from the Russian embassy in Prague. The individual was requested to leave the country within 72 hours.

"Together with our Allies, we are reducing the Russian intelligence presence in the EU," the Czech Ministry of Foreign Affairs said in a statement on Twitter.

-ABC News' Christine Theodorou

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