The British leader, who only took power in late October, urged other members of the regional Joint Expeditionary Force (JEF) grouping to follow suit "to continue the strong support" for Kyiv.

"The first is ensuring that we deliver more military aid and that military aid evolves to meet the situation that we are now facing," Sunak told the other leaders gathered in the Latvian capital, Riga.

"That means more air defence systems, it means artillery, it means armoured vehicles."

Sunak said Western nations aiding Ukraine in its war against invading Russian troops "must continue to focus on degrading Russia's capability to regroup and to resupply.

"That means going after its supply chains and removing the international support," he added, calling out Iran for supplying Moscow with arms.

Sunak also rejected heeding any unilateral calls for a ceasefire in Ukraine by the Kremlin, branding such demands "completely meaningless in the current context".

"It would be used by Russia to regroup, to reinforce their troops and until they have withdrawn from conquered territory, there can and should be no real negotiation," he added.

Ahead of his arrival, his office announced the UK would send a major new military aid package to Ukraine, highlighting hundreds of thousands of rounds of artillery ammunition it will ship.

London noted it had led the way in dispatching various types of arms to Ukraine since Russia's invasion in late February, including Multiple Launch Rocket Systems and recently 125 anti-aircraft guns.

Ukrainian President Volodymyr Zelensky joined the summit via video-link and called on JEF -- which also includes Denmark, Finland, Estonia, Iceland, Latvia, Lithuania, the Netherlands, Sweden and Norway -- to "do everything" to help defeat Russia.