Washington | Ukrainian President Volodymyr Zelenskyy says the world must not wait for November to drive back Russia's offensive against his country.

Zelenskyy made the remarks while attending this week's summit of NATO leaders in Washington.

He said the world was waiting to see what would happen in November, when voters are expected to decide between incumbent President Joe Biden and Republican opponent Donald Trump. But he said there needed to be action before then to defeat Russian President Vladimir Putin in his war against Ukraine.

Zelenskyy has proven to be an adept navigator of international relations in defence of his war-ravaged country, publicly cajoling and sometimes loudly complaining to get the military assistance it needs to defend itself against Russia's invasion.

But, as he attends the NATO summit, his most coveted prize -- membership in the military alliance -- remains elusive. The European and North American countries making up NATO are in no hurry to admit Ukraine, especially while it is engaged in active hostilities with Russia that could drag them into a broader war.

Zelenskyy, who was feted as a champion of democracy in Washington in the aftermath of Russia's 2022 invasion but was forced to plead his case for aid to US lawmakers just last year, will find himself once again in the American capital as bridesmaid.

At the NATO summit, he'll be trying to navigate a tumultuous American political landscape as President Joe Biden tries to show his strength on the world stage and ability to keep leading the alliance's most important member following a shaky debate performance against former President Donald Trump.

A NATO sceptic, Trump has criticised allies for not hitting defence-spending goals and raised concerns in Europe about continued US support for NATO and Ukraine. His Republican supporters in Congress were responsible for a monthslong delay in US military assistance, which allowed Russia to gain ground against Ukraine's depleted forces.

The stakes for Zelenskyy have never been higher as he prepared to address a Reagan Institute audience that was to include some of the most senior congressional Republicans. He got to Washington on Tuesday, a day after Russia unleashed its heaviest bombardment of Kyiv in almost four months and one of the deadliest of the war, which levelled a wing of Ukraine's biggest children's hospital.

Against that backdrop, Zelenskyy, who will have a separate meeting with Biden on Thursday, again made an urgent appeal for additional air defences shortly after arriving in Washington, writing on the social media platform X that "We are fighting for more air defence systems for Ukraine, and I'm confident we will succeed." Hours before Zelenskyy's Tuesday night address, Biden announced to great fanfare that the US and other NATO members will send dozens of air-defence systems to Ukraine in the coming months, including at least four of the powerful Patriot systems it has been desperately seeking to help fight off Russian advances in the war.

Speaking at an event celebrating the alliance's 75th anniversary, NATO Secretary-General Jens Stoltenberg urged the West to keep sending weapons and ammunition to Ukraine whatever the costs, saying the outcome of the war with Russia "will shape global security for decades to come".

But an invitation to join the alliance is not in the cards even as Russia's latest strikes have galvanised support for his country.

"We would like to see greater resolve in our partners and hear resolute responses to these attacks," Zelenskyy said on Monday in Poland before flying to the US.

US Secretary of State Antony Blinken, meeting with Ukraine's foreign minister on Tuesday, said the summit would further strengthen Ukraine's ties to NATO and "its path to membership". He noted the "despicable" Russian attack on the children's hospital.

Foreign Minister Dmytro Kuleba said the hospital strike "pretty much sets the agenda for today's meeting".

In the coming days, Zelenskyy will hear a chorus of support from countries that have poured weapons into his country, despite the recent damaging US and European lags in greenlighting more aid.

"It is critical that the world continues to stand with Ukraine at this important moment and that we not ignore Russian aggression," Biden said in a statement late on Monday, saying that US support for Ukraine is "unshakeable".

"Together with our allies, we will be announcing new measures to strengthen Ukraine's air defences to help protect their cities and civilians from Russian strikes," Biden said. "The United States stands with the people of Ukraine." Chancellor Olaf Scholz of Germany, whose country is the second-richest in NATO, also expressed solidarity with Ukraine. "Germany stands unwaveringly by the side of the Ukrainians, especially in these difficult times," he said.

Defence Secretary Lloyd Austin said last week that the US would be announcing an additional USD 2.3 billion in security assistance for Ukraine, to include anti-tank weapons, interceptors and munitions for Patriot and other air-defence systems.

In a small first step as the summit kicked off on Tuesday, Blinken said NATO allies would provide more than USD 7 million in personal protective gear, uniforms and boots specifically for female Ukrainian soldiers.