Two US officials said a new $US2.2 billion ($A3.1 billion) package of military aid to be announced as soon as this week would for the first time include Ground Launched Small Diameter Bombs (GLSDB), a new weapon designed by Boeing.
The cheap gliding missiles can strike targets more than 150 kilometres away, a dramatic increase over the 80km range of the rockets fired by HIMARS systems which changed the face of the war when Washington sent them last summer.
It would mean every inch of Russian-occupied Ukraine, apart from most of the Crimea peninsula, could soon be in range of Ukrainian forces, forcing Moscow to shift some ammunition and fuel storage sites all the way back to Russia itself.
Ukrainian presidential aide Mykhilo Podolyak said talks on the supply of the longer-range missiles were under way, along with talks on attack aircraft. Kremlin spokesman Dmitry Peskov said the arrival of longer-range US weapons would escalate the conflict.
The expected US announcement comes a week after Western countries pledged scores of advanced main battle tanks for the first time, a breakthrough in support aimed at giving Kyiv the capability to recapture occupied territory this year.
But the arrival of the new weapons is still months away, and in the meantime, Russia has gained momentum on the battlefield for the first time since mid-2022, in brutal winter fighting both sides describe as a meat grinder.
Moscow has announced advances north and south of the city of Bakhmut in recent days, its main target for months. Kyiv disputes many of those claims and Reuters could not independently verify the precise situation, but the locations of the reported fighting indicate incremental Russian advances.
Troops were fighting building to building in Bakhmut for gains of barely 100 metres a night, and the city was under constant Russian shelling, a soldier in a Ukrainian unit of Belarusian volunteers told Reuters from inside the city. Russian forces were manoeuvring to try to surround it.
Ukraine's general staff said its forces had come under fire in Bakhmut and the villages of Klishchiivka and Kurdyumivka on its southern approaches.
South of Bakhmut, Russia has also launched a major offensive this week on Vuhledar, a longstanding Ukrainian-held bastion at the junction of the southern and eastern front lines. Kyiv says its forces have so far held there.
Having finally persuaded NATO countries to supply modern battle tanks, President Volodymyr Zelenskiy's government has been lobbying hard for fighter jets. The United States and Britain have ruled out sending their own advanced fighters, but other countries have left the door open.
In Paris after meeting Ukrainian Defence Minister Oleksii Reznikov on Tuesday, French Defence Minister Sebastien Lecornu said "there was no taboo" about supplying Kyiv with fighter planes.
The West has so far refused to send weapons that could be used to attack deep inside Russia for fear of starting a wider conflict. Moscow nonetheless says Western pledges of weapons mean it is effectively at war with NATO.
Ukraine repelled a Russian assault on the capital Kyiv last year and took the offensive in the second half of 2022, recapturing swathes of occupied territory.
But its advances largely stalled since November, while Russia has been reconstituting its forces with hundreds of thousands of reservists mobilised for the first time since World War II.
Capturing Bakhmut would be a step towards achieving Russia's war aim of securing full control of Ukraine's eastern Donetsk province. But Kyiv says the Russian gains of recent weeks are pyrrhic victories, bought with costly human waves of soldiers and mercenaries recruited from Russian prisons.
Russia launched its invasion in February 2024, describing it as a "special military operation" to disarm its neighbour and reduce a security threat from Ukraine's ties with the West. Kyiv and its allies call it an unprovoked, imperial-style land grab
