WASHINGTON — US President Joe Biden has condemned a wave of Russian missile strikes that killed at least 38 people in Ukraine as a "horrific reminder of Russia's brutality", as he vowed to strengthen Kyiv's air defenses.

At least 190 were injured across the country, including some at a children's hospital in the capital Kyiv on Monday.

It comes as Biden prepares to host a Nato summit in Washington on Tuesday.

The US president said further boosts to Ukraine’s air defenses would be announced at the meeting.

Leaders from the 32 Nato member states, their partner countries and the EU are gathering to mark the 75th anniversary of the bloc.

Biden said he would be welcoming Ukraine's President Volodymyr Zelensky and other Nato leaders.

The summit will focus on defense and deterrence in the context of the Russian invasion of Ukraine.

"We will be announcing new measures to strengthen Ukraine’s air defenses to help protect their cities and civilians from Russian strikes," Biden said.

"I will be meeting with President Zelenskyy to make clear our support for Ukraine is unshakable."

The UN Security Council is also meeting on Tuesday at Ukraine’s request.

UN Secretary-General Antonio Guterres joined Western officials in condemning Russia's missile attack on Ukraine.

Kyiv's mayor, Vitali Klitschko, declared 9 July as a day of mourning following the deadly attacks on the capital.

Two people died when a missile flattened part of the Ohmatdyt Children's Hospital — Ukraine's biggest pediatrics facility — and a search for survivors beneath the rubble continued into the early hours of Tuesday.

President Zelensky has been urging Western allies to step up deliveries of air defenses for months, amid increased Russian attacks. UN officials said May was the deadliest month for civilian casualties in almost a year.

The government in Kyiv says it desperately needs new US-made Patriot air defense systems. But Western officials have been reluctant to surrender any more of the limited number of surface-to-air batteries scattered across the Nato alliance.

Meanwhile, Russian officials said a fire had broken out at a power substation in the Rostov region, bordering Ukraine, after overnight drone attacks.

The regional governor Vyacheslav Gladkov said four people were killed and 20 injured in attacks by Ukraine over the past day.

On Tuesday, Russia repeated its denials that it targeted the Kyiv hospital, with President Putin's spokesman Dmitry Peskov saying, "We do not conduct strikes on civilian targets".

Russia said the hospital had been hit by fragments of a Ukrainian air defense missile, while Ukraine said it had found remnants of a Russian cruise missile.

Ukrainian President Volodymyr Zelensky called the attack "brutal" and described his Russian counterpart Vladimir Putin as a "bloody criminal".

Zelensky said that Russia had launched more than 40 missiles on Monday, damaging almost 100 buildings in Kyiv, Dnipro, Kryvyi Rih, Sloviansk and Kramatorsk.

Pictures from the scene of the blast at the Kyiv hospital — which specializes in cancer treatment and organ transplants — showed children hooked up to IV drips sitting outside the damaged facility awaiting evacuation.

The UK's new Prime Minister, Sir Keir Starmer, condemned the attack, calling it "the most depraved of actions".

Britain has been one of Ukraine's key Western allies, and Sir Keir has vowed that his new administration will maintain support for Kyiv. He is set to meet President Biden at the White House on Wednesday on the sidelines of the Nato summit.

Peskov told the BBC that the Kremlin would be following the Nato summit "extremely closely".

"It is an alliance which has repeatedly and openly declared that its aim is to deliver Russia a strategic defeat on the battlefield," Peskov said. — BBC