US Secretary of State Antony Blinken has landed in Ukraine as weapons from a new American aid package begin arriving at the front line.
His visit comes as the country struggles to hold back a major Russian incursion near its second biggest city of Kharkiv.
America’s top diplomat is expected to meet President Volodymyr Zelensky and other officials.
Mr Blinken will deliver a message of reassurance, US officials say.
The secretary of state’s arrival on Tuesday marks three weeks since the US Congress finally agreed a new $61bn (£49bn) aid package for Ukraine.
The breakthrough followed more than a year of partisan paralysis in Washington with some Republicans adamantly opposed to the funding.
Ahead of Mr Blinken’s arrival in Kyiv, a senior US official said the American-funded weapons now arriving at the front line included air defence interceptors, artillery and ATACMS long-range precision guided missiles.
“We have already started to flow in artillery [and] long-range ATACMS that can range any part of Ukraine, and also other air defence capabilities that are meant to meet the most pressing needs, particularly with an eye towards Russia’s activities right now in Kharkiv,” the official said.
Mr Blinken arrived by sleeper train, rolling into Kyiv after a nine-hour journey from the Polish border.
He touched down on Monday in the south-eastern Polish town of Rzeszów, whose airport is now a major logistical hub bringing defence supplies and humanitarian aid into Ukraine.
The airfield’s perimeter bristles with US Patriot missile defence batteries – a stark reminder of America’s role in shoring up defences at Nato’s frontier, more than two years into the war in Ukraine.
Mr Blinken will deliver a message of “strong reassurance” to the Ukrainians “in a difficult moment”, a US official said. This will include talks on helping the country take back the military “initiative”, said the official.
Ukraine was facing not only a “grinding battle on the eastern front”, the official added, but also the latest cross-border attack towards Kharkiv.
Asked by the BBC whether the delay in weapons supply by Congress could have contributed to Moscow’s decision to carry out the assault, the official said they would not “draw any direct correlation”, but added “the Ukrainians have certainly been in a more difficult position because they waited a long time for this assistance”.
Washington hopes a surge of US-supplied arms will enable Ukraine to move towards an “active defence” against the Russians and become “increasingly more confident holding their positions, pushing back as they get more assistance”.
