Blinken has said he wants to hear directly from Ukrainian President Volodymyr Zelenskiy and others what Kyiv's goals in the war are and what Washington can do to help it achieve them.
"I think it's a critical moment for Ukraine in the midst of what is an intense fall fighting season with Russia continuing to escalate its aggression," Blinken told a joint news conference with Lammy in London on Tuesday.
President Volodymyr Zelenskiy is calling for the West to allow Ukraine to use longer-range missiles. (AP PHOTO)
Zelenskiy has been pleading for Western countries to supply longer-range missiles and to lift restrictions on using them to hit targets such as military airfields deep inside Russia.
US officials have voiced doubts about such a move amid fears of instigating a direct conflict between the West and Russia, but overnight US President Joe Biden suggested there was room for compromise.
Biden said his administration was "working that out now" when asked if the United States would lift restrictions on Ukraine's use of long-range weapons in its war against Russia.
The speaker of Russia's lower house of parliament, Vyacheslav Volodin, said on Wednesday that Moscow would consider the US and its allies to be parties to the war if they allowed Kyiv to use long-range weapons.
Blinken has declined to say whether Washington would allow the use of long-range weapons deep inside Russia, but said multiple factors went into the consideration of this decision rather than just looking at it as a weapons system.
President Joe Biden suggested there was room for compromise on Ukraine using long-range weapons. (AP PHOTO)
"It's not just the system itself that counts. You have to ask: can the Ukrainians effectively use it, and sometimes that requires significant training, which we've done. Do they have the ability to maintain it?" Blinken said.
On the battlefield more than two-and-a-half years since the invasion began, Ukrainian forces are being stretched by a better armed and bigger foe, as they try to fend off Russian gains in the east where Moscow is focusing its attacks.
In a bid to seize back some of the initiative and divert Russian forces, Kyiv in August sent troops into Russia's Kursk region in an audacious large-scale cross-border incursion.
Blinken's visit comes a day after he said Russia has received ballistic missiles from Iran and will likely use them in Ukraine within weeks, warning that co-operation between Moscow and Tehran threatens wider European security.
The deepening military co-operation between Iran and Russia is a threat for all of Europe, Blinken said, adding Washington had privately warned Iran that providing ballistic missiles to Russia would mark "a dramatic escalation".
Ukrainian forces are being stretched as they try to fend off Russian gains in the east. (AP PHOTO)
The US imposed fresh sanctions on Iran on Tuesday over the transfer.
Thousands of civilians have died in the war, which Russia started with a full-scale invasion on Ukraine in February 2022.
Millions of Ukrainians have also been displaced, while many cities and villages have become piles of rubble.
Russia has escalated its drone and missile attacks on Ukraine in recent weeks, while Ukraine has also sent hundreds of long-range attack drones deep into Russian territory.
Later in September, Zelenskiy travels to the United States and will present a plan to Biden and his two potential successors in November's presidential election that he hopes will bring the end of the war closer.
