US Secretary of State Antony Blinken and British foreign minister David Lammy have arrived in Kyiv for meetings with senior Ukrainian government officials at a critical juncture in the war against Russia.
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.
Zelenskiy is likely to renew appeals to his allies to allow Ukraine to fire Western missiles including long-range US ATACMS and British Storm Shadows deep into Russian territory to limit Moscow's ability to launch attacks.
After arriving on Wednesday, Blinken and Lammy are expected to push Ukraine for more information on its strategic aims as they consider whether to give the go-ahead, according to Western sources.
There is nervousness in Washington and some European capitals that doing so would provoke Russia towards a direct conflict with the West, while officials also recognise that Ukraine needs more help if it is to swing the war in its favour.
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 Moscow would consider the United States 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 give permission, but said multiple factors went into any decision.
"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.
After making rapid progress initially, Ukrainian advances have stalled, and on Wednesday a senior Russian commander said his forces had taken back control of about 10 settlements.
The economic damage from the Kursk incursion totals at least $US931 million ($A1.4 billion), regional governor Alexei Smirnov said on Wednesday.
More than 150,000 people have been forced to flee since the start of Ukraine's attack, he said.
Blinken's visit to Kyiv comes a day after he said Russia has received ballistic missiles from Iran and will likely use them in Ukraine within weeks, warning co-operation between Moscow and Tehran threatened wider European security.
Russia and Iran both deny Blinken's assertion.
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".
The US imposed fresh sanctions on Iran on Tuesday over the alleged 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.
