NATO leaders meet Wednesday for their 75th anniversary, seeking ways to ramp up support for Ukraine as deadly Russian strikes and political uncertainties in the West stir new concerns.

With the pomp of a summit in Washington, President Joe Biden is aiming to rally the West and also reassure US voters amid intense pre-election scrutiny on whether at 81 -- six years older than the alliance -- he remains fit for the job.

Kicking off three days of events for the 32-nation alliance with a celebration Tuesday evening, Biden announced a new air defense system for Kyiv and urged unity against Russian President Vladimir Putin, who launched the Ukraine invasion in 2022.

"Make no mistake. Ukraine can -- and will -- stop Putin," Biden said forcefully to applause.

On the eve of the summit, Russia fired a barrage of missiles on Ukraine, killing dozens, including in Kyiv where a children's hospital was reduced to debris.

Biden has invited Ukrainian President Volodymyr Zelensky to the summit as well as the leaders of four key Pacific partners -- Japan, South Korea, Australia and New Zealand -- as he seeks to increase NATO's role in managing a rising China.

But the US president himself is facing a tough election challenge from Donald Trump, who has loudly questioned the utility of NATO and mused on forcing a peace deal in which Ukraine would surrender land to Russia.

'Greatest risk'

Zelensky in Washington thanked Ukraine's backers for the promise of new air defenses -- and urged the United States and others to go further to help defeat Russia.

NATO's outgoing secretary general, Jens Stoltenberg of Norway, acknowledged the question marks, after Trump's allies in the US Congress forced a delay of months in approving new weapons for Ukraine.

"Ukraine has shown remarkable courage and NATO allies have provided unprecedented support. But let's be honest -- not even our support for Ukraine has been a given," Stoltenberg said.

"Remember -- the biggest cost and the greatest risk will be if Russia wins in Ukraine. We cannot let that happen."

Other leaders attending the summit include Hungarian Prime Minister Viktor Orban, one of Putin's closest partners in the West, who ahead of Washington went to Ukraine, Russia and China on a self-described peace mission criticized by Brussels and Washington.

Another Asian partner of the US, Indian Prime Minister Narendra Modi, met Putin on the eve of the NATO summit and is not part of the Washington talks.

Leaders on Wednesday will formally convene the alliance's North Atlantic Council inside downtown Washington's convention center.

Biden, Secretary of State Antony Blinken and Defense Secretary Lloyd Austin will later welcome their counterparts for gala dinners around the Washington area, which is in the throes of a searing heat wave.

One new NATO leader is British Prime Minister Keir Starmer, who is visiting days after taking office in a landslide victory by his Labour Party.

He will meet both Biden and Zelensky and is expected to confirm Britain's strong support for Ukraine.

Reassurances for Ukraine

Ukraine has been seeking firm assurances that it will one day join NATO, which considers an attack on any member an attack on all.

Ukraine's membership enjoys wide backing from Baltic and Eastern European nations still haunted by decades under the Soviet yoke.

But Biden and German Chancellor Olaf Scholz have led opposition, concerned that the alliance would effectively be entering war with nuclear-armed Russia as it occupies swathes of Ukraine.

Zelensky, who has achieved hero status in much of the West for his media-savvy defiance of Russia, voiced open annoyance at the last NATO summit in Lithuania at the failure to provide a clearer path to membership.

In Washington, the US is seeking to play down his expectations, speaking of creating a "bridge" to membership but making clear quick entry is not on the cards.

Estonian Defense Minister Hanno Pevkur said negotiations were ongoing on the final language and that he was hopeful for a word such as "irreversible" to describe Ukraine's path to NATO.

Putin has repeatedly accused the West of antagonizing Russia by entertaining NATO membership for Ukraine, whose separate identity he has rejected.

Ukraine has also been clamoring for greater air defenses to protect cities being barraged by Russia.

Biden promised Monday an additional Patriot system, on top of two new systems being given by Germany and Romania and one which the Netherlands has said it is putting together with parts from other allies.