President Volodymyr Zelensky of Ukraine compared his country’s fight against Russia to the biblical battle of David and Goliath, telling dozens of western officials gathered in Munich for a security conference on Friday that western weapons would be the key to defeating “the Russian Goliath”.

Zelensky’s address came at the opening of the annual three-day Munich Security Conference, where Ukraine is dominating the discussions.

Officials, who include US Vice-President Kamala Harris and secretary of state Antony J. Blinken, are aiming to show unity. But that is likely to be tested as the war grinds on, and the cost of sustaining the Ukrainian fight with ever more and more powerful weapons against a larger opponent threatens to create strains.

Zelensky acknowledged the real possibility of “fatigue” among Ukraine’s allies, but stressed that the “united Davids” of the free world would prevail. “Being David is having that sling to win,” Zelensky said in a video message.

“We do not yet have that sling.” He said that was why weapons deliveries must be accelerated, telling the audience, “There is no alternative to speed.” “Delay has always been, and still is, a mistake,” he said.

Several prominent heads of state were in attendance, including President Emmanuel Macron of France, Chancellor Olaf Scholz of Germany and Prime Minister Rishi Sunak of Britain.

President Joe Biden attended the conference as vice-president and as a private citizen during the Trump administration but has sent Harris each of the past two years.

The Ukrainian leader spoke as Russia has stepped up its offensive in eastern Ukraine. In recent weeks, Moscow has rushed tens of thousands more troops, many of them inexperienced new recruits, to the front lines as President Vladimir V. Putin’s forces seek to demonstrate progress before the anniversary of Russia’s invasion on February 24.

With battles looming, Ukraine’s allies have been working to come up with ways to provide Kyiv with the supplies it will need for the fight ahead. Already, allies have given all manner of different western weapon systems to Kyiv’s war effort, most recently pledging to supply it with battle tanks.

Having won the commitment of tanks and armoured fighting vehicles in January, Ukrainian officials quickly turned to the next item on their wish list: fighter planes. Zelensky expressed thanks for allies’ assistance to date, but noted that he had sought support at the previous year’s conference, in the days ahead of Russia’s invasion.