(NewsNation) — At least 31 people were killed in cities across Ukraine after dozens of Russian missiles struck apartment buildings and a large children’s hospital in the capital.

Now, as world leaders prepare to gather at a NATO summit commemorating the 75th anniversary of the military alliance, former U.S. Ambassador to Ukraine William Taylor says Ukraine “needs reassurance” of U.S. support.

“They’re looking for President Biden for leadership. And so far, that has been the response, that has been the leadership the United States has provided. U.S. allies are looking for that to continue,” Taylor said. “We are their biggest ally. They know it. We know it. We need to provide it. And so I got a couple of calls after the debate, but they just need reassurance that this is going to continue the support that they needed all along.”

Reeling from his disastrous June 27 debate performance and struggling to hold his reelection campaign together, Biden says people should look to his interactions at the NATO summit for proof that he is still strong and vigorous enough to lead.

The latest attack was Russia’s heaviest bombardment of Kyiv in almost four months, hitting seven of the city’s 10 districts. At least seven people were killed in the capital, including two staff members at the hospital. Strikes in Kryvyi Rih, Zelenskyy’s birthplace in central Ukraine, killed 10.

The attack on the Okhmatdyt Children’s Hospital caused debris to fall into heart patients’ open chests in the middle of surgery. Cancer patients had their beds wheeled into parks and onto the streets.

“This children’s hospital is only the latest atrocity. Putin, as you know, has already been indicted by the International Criminal Court as a war criminal for these kinds of actions. So this is a continuation; this is not, sadly, new. This is demonstrating what kind of opponent the Ukrainians are fighting,” Taylor told NewsNation.

Zelenskyy said during a visit to Poland that he hopes the summit will provide Ukraine with more air defense systems.

The Associated Press contributed to this report.