KYIV, Ukraine (AP) — The death toll from a weekend Russian missile strike on an apartment building in the southeastern Ukrainian city of Dnipro has risen to 37, authorities said Monday, as Western analysts pointed to signs indicating the Kremlin was preparing for a drawn-out war in Ukraine after almost 11 months of fighting.

The victims from Saturday’s strike on the multi-story residential tower included two children, Ukraine’s National Police reported, and 15 children are among the 75 injured. The rescue and search operation was ongoing, with 39 people, including six children, taken from the ruins so far, the police said in a statement.

About 1,700 people lived in the apartment building. Residents said there were no military facilities at the site. The reported death toll made it the deadliest single attack on civilians since before the summer, according to The Associated Press-Frontline War Crimes Watch project.

The European Union’s foreign policy chief, Josep Borrell, called the strike, and others like it, “inhumane aggression” because it directly targeted civilians. “There will be no impunity for these crimes,” he said in a tweet Sunday.

Asked about the strike Monday, Kremlin spokesman Dmitry Peskov said the Russian military doesn’t target residential buildings and suggested the Dnipro building was hit as a result of Ukrainian air defense actions. The Ukrainian military said Sunday that it did not have the means to intercept the type of Russian missile used in Saturday’s strike.

The strike on the building came amid a wider barrage of Russian cruise missiles across Ukraine.

Fierce fighting continued to rage in Ukraine’s eastern Donetsk province, where military analysts have said both sides are likely suffering heavy troop casualties. No independent verification of developments was possible.

Donetsk and neighboring Luhansk province make up the Donbas, an expansive industrial region bordering Russia that Russian President Vladimir Putin identified as a focus from the war’s outset. Moscow-backed separatists have been fighting Kyiv’s forces there since 2014.

The Russian and Belarusian air forces began a joint exercise Monday in Belarus, which borders Ukraine and served as a staging ground for Russia’s Feb. 24 invasion of Ukraine.The drills are set to run through Feb. 1, the Belarusian Defense Ministry said. Russia has sent its warplanes to Belarus for the drills.

The Institute for the Study of War, a Washington think tank, reported signs of the Kremlin taking steps to turn its Ukraine invasion into “a major conventional war” after months of embarrassing military reversals.

What Moscow calls “a special military operation” aimed to capture the Ukrainian capital, Kyiv, within weeks and to install a Kremlin-friendly regime there, but Russian forces ultimately withdrew from around Kyiv, the think tank said. Then came a successful Ukrainian counteroffensive in recent months before the onset of winter slowed military advances.

“The Kremlin is likely preparing to conduct a decisive strategic action in the next six months intended to regain the initiative and end Ukraine’s current string of operational successes,” the Institute for the Study of War said in a report late Sunday.

It noted reports indicating the Russian military command was in “serious preparations” for an expanded mobilisation effort, conserving mobilised personnel for future use, while seeking to boost military industrial production and reshuffling its command structure.

That means Ukraine’s Western allies “will need to continue supporting Ukraine in the long run,” the think tank said.

NATO member nations have sought in recent days to reassure Ukraine that they will stay the course. The United Kingdom has pledged tanks and the US military’s new, expanded combat training of Ukrainian forces began in Germany on Sunday.