Russia used an intercontinental ballistic missile (ICBM) against Ukraine for the first time, Kiev’s air force said Thursday, in a move likely intended to send a message from the Kremlin at a crucial point in the nearly three years of war .

The ICBM was launched in the central Ukrainian city of Dnipro from Russia’s southwestern Astrakhan region, the Ukrainian air force said, adding that Moscow separately fired a Kinzhal hypersonic missile and seven Kh-101 cruise missiles.

At the time of writing this article, the Russian Defense Ministry had not acknowledged the reports, while the Kremlin and Russian Foreign Ministry dismissed questions about the alleged ICBM use in a Thursday briefing.

The attack comes shortly after the US closed its embassy in the capital after receiving “specific information about a possible significant airstrike” on Wednesday.

US officials said earlier this week that Washington had approved Ukraine’s use of US Army Tactical Missile Systems (ATACMS) against Russian territory, a reversal of long-standing White House policy. Russia said Ukraine has used six ATACMS in Russia’s Bryansk border region in an “escalation” of the conflict.

Britain has not yet publicly confirmed whether it has given Ukraine the green light to fire British-made Storm Shadow cruise missiles at Russia, but several British media reported that Kiev had used the air-launched missiles for the first time.

Earlier this week, Moscow updated its nuclear doctrine to justify a nuclear attack on a country without nuclear weapons, if that country attacks Russia and is backed by a nuclear force. The change came on the same day that Ukraine marked 1,000 days of all-out war with its neighbor, amid concerns about how U.S. support for Ukraine will change once President-elect Donald Trump steps back into the White House in January.

Jim Townsend, a former Pentagon official, said Thursday he was “not surprised” that Russia would launch a conventionally armed ICBM in its war effort against Ukraine.

“It’s a step forward in terms of the delivery vehicle,” Townsend said in response to a message Newsweek question during a panel at the Royal United Services Institute, a British think tank.

“There are a lot of things Putin is doing right now to express his displeasure with ATACMS,” Townsend said, but also to set the tone for the incoming Trump administration.

What is an intercontinental ballistic missile and is it a nuclear weapon?

An ICBM is a ballistic missile that can travel distances of more than 5,500 kilometers, or about 3,417 miles. They are considered a strategic weapon capable of carrying nuclear warheads.

Their long range means they can threaten an enemy’s territory from thousands of miles away. The US is currently upgrading its Minuteman III ICBMs, which form the ground-based part of its nuclear triad, to Sentinel ICBMs.

The ICBM reported by Ukraine is believed to be a road-mobile RS-26, also known as the Rubezh missile. It can carry a nuclear or conventional payload, or have multiple independently targetable reentry vehicles that carry explosives to different targets.

However, there are questions about whether an RS-26 was used, or whether it was a medium-range ballistic missile capable of shorter ranges. Ukrainian President Volodymyr Zelensky said the “characteristics” of the missile, including its speed and altitude, had indicated it was an ICBM, but investigations were ongoing.

The RS-26 has been tested at ranges below the classification for an ICBM, which has raised concerns that Russia has violated the Intermediate-Range Nuclear Forces (INF) Treaty. This treaty, signed between the US and the then Soviet Union in the 1980s, banned ground-launched ballistic missiles and cruise missiles with a range of more than 500 kilometers and less than 5,500 kilometers.

The Rubezh was never officially put into service and is still considered under development.

A former Ukrainian official said this Newsweek that the ICBM aimed at Dnipro carried approximately 1,200 kilograms of explosives, and “acts like a cluster bomb”, dividing into six separate warheads before hitting the target. The Ukrainian Air Force declined to comment when contacted Newsweek.

Video footage of the attack appears to show six different clusters of munitions, which reportedly hit the Yuzhmash Defense and Space Center. Newsweek could not independently verify this.

Serhiy Lysak, the regional governor of the Dnipropetrovsk region covering Dnipro, said an industrial building, several houses, garages and a rehabilitation center were damaged. Two people were injured, Lysak said.

Has an ICBM been used before?

Much is still unknown about the launch, but if confirmed it would be the first combat use of a conventional ICBM or intermediate-range ballistic missile in history.

Analysts say that if Russia were to use a Rubezh missile, it would not be the practical choice for a target like the Dnipro facility.

“The RS-26 was designed to carry nuclear warheads, but that clearly did not happen in this attack,” said William Freer, research fellow at the British think tank Council on Geostrategy.

“Russia likely used the RS-26 as a way to intimidate Ukrainian supporters by escalating tensions over the deployment of a nuclear-capable ballistic missile, one that could hit European capitals,” Freer added. “Its use is a signal rather than based on a military need.”