Ukraine said on Thursday Russia had launched against its territory an intercontinental ballistic missile (ICBM) designed to carry nuclear warheads.

But while warning that such a step would make a major escalation, Ukraine's European allies did not confirm Kyiv's initial assessments that such a weapon had been fired.

A US official, who asked not to be named, said Russia's strike on Ukraine was not an ICBM, but an "experimental" medium-range ballistic missile.

In an address to the nation late Thursday, Russian President Vladimir Putin confirmed that Russia had used a new, experimental "hypersonic" medium range non-nuclear ballistic missile named "Oreshnik" ("Hazel") in the arrack on Dnipro.

- What was fired?

Analysts and now the United States have pushed back on the initial claims from Kyiv that Moscow had launched the nuclear capable ICBM as part of a barrage towards the central city of Dnipro.

Using such a missile at such short range would be a hugely profligate use of valuable resources. "My take is that one must be sceptical and cautious," wrote weapons expert Pavel Podvig, director of the Russian Nuclear Forces Project.

While not naming the missile used or giving technical specifications, the US official said Russia "likely possesses only a handful of these experimental missiles."

"Ukraine has withstood countless attacks from Russia, including from missiles with significantly larger warheads than this weapon," the official said.

In London, a spokesman for British Prime Minister Keir Starmer told reporters Russia's strike on Ukraine was a "ballistic missile" with "a range of several thousand kilometres", the first time Moscow had used such a weapon in the war.

- What is the context?

Tension has been building between Moscow and Kyiv's allies in the West since Ukrainian forces struck Russian territory with Western-supplied long-range weapons on Tuesday after getting the green light from Washington.

US President Joe Biden gave Ukraine the go-ahead to fire the missiles into Russian territory for the first time while Washington will soon provide Ukraine with antipersonnel land mines to shore up its defences against Russian forces.

Biden is moving to boost Ukraine's war effort in the final two months of his administration, before Donald Trump, who has repeatedly promised to end the war quickly, takes power in January.

"The United States will continue to surge security assistance to Ukraine to strengthen capabilities, including air defence, and put Ukraine in the best possible position on the battlefield," the official said.

In London, the British government spokesman said: "It is another example of reckless behaviour from Russia, which only serves to strengthen our resolve in terms of standing by Ukraine for as long as it takes."

- What message is Moscow seeking to send?

Despite the initial confusion on the nature of the missile fired, it is clear that the strike on Dnipro was unusual and aimed at sparking the maximum attention from Kyiv and its allies.

"We are really on something unprecedented, and it is much more a political act than a military act. The cost-effectiveness ratio of the attack is zero," says Heloise Fayet, a researcher at the French Institute of International Relations (IFRI).

"This change of scale is significant," she said, adding this was "the first use by the Russians on the battlefield of a missile with a range greater than 2,000 kilometres."

But the use of this missile "will not change the situation significantly on the operational level. They obviously have very few and they are expensive."

Local authorities said an infrastructure facility was hit in Dnipro and two civilians were wounded.

For Nick Brown, of British defence analysis organisation Janes, "this is really about sending an escalatory message or warning, an expensive and potentially dangerous way for Russia to rattle its sabre."

According to the US official: "Russia may be seeking to use this capability to try to intimidate Ukraine and its supporters... but it will not be a game changer in this conflict," the US official said.