"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.

Ukraine accused Russia on Thursday of having launched a nuclear-capable intercontinental ballistic missile (ICBM) as part of a barrage on the central city of Dnipro.

The US official said the missile used in the strike was not an ICBM but an "experimental medium-range ballistic missile" and 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.

The United States briefed Ukraine and allies in recent days about Russia's possible use of the weapon, the official said.

The US official also recalled that President Joe Biden had announced plans earlier this year to provide Ukraine with hundreds of Patriot and AMRAAM missiles to strengthen its air defenses.

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

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.

Ukrainian President Volodymyr Zelensky said the missile strike on Dnipro bore "all the characteristics" of an ICBM attack and accused the Kremlin of "using Ukraine as a testing ground."

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