DNIPRO, Ukraine — Russian missiles rained down on Ukrainian cities in a major attack Saturday, killing at least 12 in a strike on an apartment building in the central city of Dnipro — the latest salvo in a brutal war that has convinced Kyiv's Western allies to send increasingly advanced military equipment to Ukraine.

Dozens of first responders scrambled through the wreckage of the apartment block, searching for survivors. Rescuers battled smoke billowing from the flattened multistory building, passing ladders through debris that stood several stories high.

At least 73 were wounded in the attack, according to Ukraine's top military commander, including 14 children. At least 38 had been rescued.

The toll could rise, Kyrylo Tymoshenko, deputy head of Ukraine's presidential office, suggested in a Telegram post. Up to 200 people, including 50 children, lived in apartments in the destroyed entrance, he said. More than 1,000 residents may need emergency shelter.

Earlier, explosions shook Kyiv residents awake in what Ukraine's air force said was "most likely" a ballistic missile attack. Ukraine lacks the capability to detect ballistic missiles, so Kyiv residents heard sirens only after the attack. The city's mayor said missile fragments landed in a nonresidential part of the city, sparking a fire that caused no casualties.

Ukraine's air force said it had shot down 25 out of 38 missiles launched in Saturday's attack. But rockets hit energy infrastructure in Kharkiv, Kyiv, Zaporizhzhia and other regions, prompting Ukraine to introduce emergency shutdowns "in most regions," Energy Minister Herman Halushchenko said in a Facebook post.

"The next few days are going to be difficult," he added.

Maksym Kozytsksyy, head of the Lviv regional administration, said around 40 percent of the region, or about 300,000 homes, were without power.

The attack came as Britain confirmed plans to send heavy battle tanks to Ukraine, answering a long-standing request from Kyiv as its fight against Russia's invasion approaches the one-year mark with no signs of abating.

British Prime Minister Rishi Sunak told Ukrainian President Volodymyr Zelensky in a phone call Saturday that his country would provide Challenger 2 tanks, along with additional artillery systems, according to a news release from 10 Downing Street.

The announcement marks a significant escalation of military aid to Ukrainian forces as they seek to take back more territory and fend off a potential Russian springtime offensive. Western allies had previously held back, partly out of fear of provoking a broader confrontation with Russia.

It's unclear how many tanks Britain will send and when they might arrive. Previous reports indicated Britain would provide about 10 tanks.

The action is "entirely symbolic," said retired colonel Mark Cancian, a senior adviser with the Center for Strategic & International Studies' International Security Program. "Britain only has about 250 of those tanks, so it cannot send many without severely weakening its own forces."

But Ukraine hopes the move will encourage other allies to follow suit. In particular, Kyiv has sought German-made Leopard 2 tanks — more than 2,000 of which are scattered across Europe.

"Always strong support of the UK is now impenetrable," Zelensky tweeted on Saturday, adding that he had thanked Sunak "for the decisions that will not only strengthen us on the battlefield, but also send the right signal to other partners."

Russia's embassy in London warned that the move would "only serve to intensify combat operations," saying the tanks would become "legitimate large-scale targets."

Sunak's announcement came a week after the United States, Germany and France agreed to send advanced infantry fighting vehicles to Ukraine.

Ukrainian officials expressed gratitude for those vehicles, but asked for heavy tanks as well. Kyiv's forces have so far been using Soviet-era tanks, such as the T-64 and T-72.

Since Ukrainian forces took back large swaths of territory from Russia in sweeping counteroffensives this fall, the war has essentially stalled along a front line stretching hundreds of miles across eastern and southern Ukraine. Russia claimed Friday to have captured Soledar, a small salt-mining city in the Donetsk region — what would be its first significant territorial gain in several months. Ukraine's military said fighting was ongoing.

Those ground battles over territory are separate from the punishing missile strikes Russia has unleashed on cities under Ukrainian control, which have reduced homes and hospitals to rubble. Many of those strikes have targeted critical energy infrastructure, plunging millions of Ukrainians into the cold and dark as winter took hold. Ukrainian authorities have described the wave of attacks as a campaign of terror.

In a televised address Saturday evening, Zelensky said the only way to stop "Russian terror" was through "those weapons that are in the warehouses of our partners and that our troops are so waiting for."

The Challenger 2 is the British Army's main battle tank. Designed to destroy other armored vehicles, the tank has heavy armor and a 120mm rifled tank gun, as well as a 7.62mm chain gun and a separate mounted machine gun. The British Army used it in military operations in Bosnia, Kosovo and Iraq.

The tank is built to cross open terrain, which could prove especially useful in the fields of eastern Ukraine. It is capable of carrying out strong, rapid advances that shock enemy forces.

"With NATO-type tanks, we will move towards victory much faster," Ukrainian Defense Minister Oleksii Reznikov said in a statement posted to the ministry's Telegram channel.

Analysts warned that the Challenger 2 can be difficult to use and maintain.

The tanks "would provide quite a lot of logistical challenges to the Ukrainians, because these are very heavy vehicles," said Sonny Butterworth, an analyst at Janes, the intelligence firm. "They're going to have to be able to support these vehicles in the field appropriately, otherwise they won't be able to deploy them to where they need to go."

Complicating matters, the Challenger 2 uses a rifled gun that differs from the NATO standard.

Poland indicated Wednesday that it intends to transfer a company of Leopard 2s to Ukraine as part of a broader package supported by an international coalition. But the re-export of the German-made tanks requires approval from Berlin, which German Chancellor Olaf Scholz has not yet granted.

The United States is similarly hesitant. "We absolutely agree that Ukraine does need tanks," Laura Cooper, the U.S. deputy assistant secretary of defense, told reporters earlier this month. But she raised concerns about the ability of Ukrainian forces to look after Abrams tanks.

"Certainly we know that the Abrams tank, in addition to being a gas guzzler, is quite challenging to maintain," she said.

Sunak told Zelensky he and his government would work "intensively" with international partners to send more military aid, the Downing Street statement said. Defense ministers from dozens of countries will gather Friday for a meeting of the U.S.-led Ukraine Defense Contact Group in Germany, where they will discuss Ukraine's defense needs.

- - -

Stern reported from Mukachevo. Parker reported from Washington. The Washington Post's Andrea Salcedo, Ellen Francis, Francesca Ebel and Stefanie Le contributed to this report.