US President Joe Biden has condemned a wave of Russian missile strikes that killed at least 41 people in Ukraine as a “horrific reminder of Russia’s brutality”, as he vowed to strengthen Kyiv’s air defences.
At least 166 were injured across the country, including some at a children’s hospital in the capital Kyiv on Monday.
It comes as Mr Biden prepares to host a Nato summit in Washington on Tuesday.
The US president said further boosts to Ukraine’s air defences would be announced at the meeting.
Leaders from the 32 Nato members states, their partner countries and the EU are gathering to mark the 75th anniversary of the bloc.
Mr Biden said he will be welcoming Ukraine’s President Volodymyr Zelensky and other Nato leaders.
The summit will focus on defence and deterrence in the context of the Russian invasion of Ukraine.
“We will be announcing new measures to strengthen Ukraine’s air defences to help protect their cities and civilians from Russian strikes,” Mr Biden said.
“I will be meeting with President Zelenskyy to make clear our support for Ukraine is unshakeable.”
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 paediatrics 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 defences 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 defence 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 Monday, Russia denied targeting the Kyiv hospital, saying it had been hit by fragments of a Ukrainian air defence 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”.
Mr 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 specialises 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.