Mr Sullivan told the annual Yalta European Strategy conference via video link that a decision on changing the terms of use for Western-made missiles would be made in the context of a wider “plan to win the war” that Mr Zelensky intends to present to Mr Biden in New York.
“I do believe that we need a comprehensive strategy for winning this war, and that’s what president Zelensky says he’s going to bring, so we’re looking forward to sitting down and talking to him about that,” he said.
Five former British defence ministers and a former prime minister have now urged Sir Keir to unilaterally allow Ukraine to fire British-made Storm Shadow long-distance missiles at Russia – rather than wait for Mr Biden to make a decision.
Grant Shapps, Ben Wallace, Gavin Williamson, Penny Mordaunt, Liam Fox and Boris Johnson have said that any more delays will “play into Russia’s hands”.
Mr Sullivan has been a high-profile spokesman and security adviser for the US throughout the war but his more cautious approach over authorising Western missiles to be fired at Russia has reportedly caused a split with the more hawkish Antony Blinken, the US secretary of state.
Storm Shadow missiles, which have a range of around 150 miles, have been credited with turning the tide of the war by allowing Kyiv to hit Russian command centres and supply depots in occupied Ukraine deep behind the front lines.
‘Complex logistic issues’
Military supplies from the US have been vital for Ukraine’s war effort but some arms shipments have been delayed over the past month, delays that Mr Sullivan blamed on “difficult and complex logistic issues”.
“This is not a question of political will,” he said. “But given what Ukraine is up against, we need to do more and do it better.”
Mr Zelensky has increased his criticism of these slow military aid deliveries from Ukraine’s Nato allies and on Saturday he said that “every delay in military aid packages has consequences on the front”.
On the front lines, Russian military bloggers reported that Russia has now launched a major counter-attack against Ukraine’s incursion into its southern Kursk region.
According to the Two Majors channel, the Russian attack has “reduced the enemy’s control zone with a decisive onslaught” although this has been denied by Ukraine.
The British Ministry of Defence confirmed that Russian forces were trying to push back the Ukrainian invasion and had recaptured some ground in the Kursk region.
“Spearheaded by airborne and naval infantry… Russian forces have attacked Ukrainian positions in the west of the salient and have highly likely retaken several villages,” it said.
To the south east, reports said that Russian forces were also making slow progress towards the strategically important town of Pokrovsk on the front line running through Donbas. Russian military bloggers reported that Russian forces were trying to trap Ukrainian forces in a pocket.