KRAMATORSK, Ukraine — Russian missiles slammed into Kramatorsk in eastern Ukraine on Thursday, striking a city that is a key base of Ukrainian military operations, amid warnings from Kyiv that Moscow was opening a new offensive in the 11-month-old war.
The strike came hours before President Vladimir V. Putin of Russia was expected to rally domestic support for his invasion of Ukraine in a speech on the anniversary of the Soviet triumph over the Nazis at Stalingrad, a decisive battle of World War II and one that many Russians view as a symbol of wartime heroism.
Russian attacks were intensifying in Kramatorsk, a longtime command center for the Ukrainian military and a staging ground for Ukraine’s defense of the city of Bakhmut, which Russia has moved closer to capturing after months of brutal fighting. The fall of Bakhmut would be Moscow’s first significant military victory since the summer, although it has come at a huge cost in Russian and Ukrainian lives.
President Volodymyr Zelensky of Ukraine has said that a large Russian troop buildup in occupied parts of eastern Ukraine, along with a sharp increase in artillery strikes in the east, signals the start of a new Russian offensive.
On Wednesday night, at least three people were killed and more than a dozen others wounded when a rocket slammed into a four-story apartment complex in Kramatorsk, turning much of the building into a smoking ruin.
As rescuers were digging furiously through the rubble on Thursday, trying to find an entry into a basement where residents may have been hiding, there was a flash and two more missiles hit nearby, sending firefighters running in all directions.
One missile struck a courtyard, mangling several vehicles and a row of garages, and another stuck in the middle of the road. Residents fled to basements as the police warned that additional missiles were coming.
The head of the regional military administration, Pavlo Kyrylenko, said that five people were wounded in the strikes on Thursday, which hit a school, a clinic and more than a dozen buildings.
At a hospital near one blast site, Anna Olendarenko, 51, said that two of her friends, a married couple, were injured, the husband suffering a serious concussion and the wife a broken arm.
“Horrible doesn’t even describe it,” she said. “You can’t wrap your head around it.”
Kramatorsk is the largest Ukrainian city near the epicenter of the fight for the eastern area known as Donbas. It is a hive of military activity, with the numbers of soldiers and armored personnel carriers growing in recent days. Bakhmut is about 20 miles away, and the entire area comes under bombardment by Russian ordnance almost daily.
It was unclear why the apartment building might have been targeted. At the blast site, the mangled and scorched remains of several vehicles appeared as if they could belong to the military.
In April, at least 50 people were killed and many more were wounded in a missile assault on the Kramatorsk train station. The assaults have continued: A Russian missile landed just outside a kindergarten in the city last week, leaving a gaping crater. On Wednesday, the Ukrainian prosecutor general’s office said that it had opened a war crimes investigation over the latest attack.
“This is not a repetition of history; this is the daily reality of our country,” Mr. Zelensky said in a statement after the attack on Wednesday.
Carly Olson in New York and Matthew Mpoke Bigg in London contributed reporting.