President Vladimir Putin has said that Russia will keep testing its new Oreshnik hypersonic missile in combat and has a stock ready for use.
Mr Putin was speaking a day after Russia fired the new intermediate-range weapon into Ukraine for the first time, a step he said was prompted by Ukraine's use of US ballistic missiles and British cruise missiles to hit Russia.
The Kremlin leader described the missile's first use as a successful test and said more would follow.
"We will continue these tests, including in combat conditions, depending on the situation and the nature of the security threats that are created for Russia," he said in televised comments to defence officials and missile developers.
"Moreover, we have a stock of such products, a stock of such systems ready for use."
A US official, however, said the weapon Russia used was an experimental one. The official said Russia has a limited number of them and that this is not a capability that Russia is able to regularly deploy on the battlefield.
Intermediate missiles have a range of 3,000-5,500 km, which would enable them to strike anywhere in Europe or the western United States from Russia.
Security experts said the novel feature of the Oreshnik missile was that it carried multiple warheads capable of simultaneously striking different targets - something usually associated with longer-range intercontinental ballistic missiles designed to carry nuclear warheads.
Ukraine said the missile reached a top speed of more than 13,000kph and took about 15 minutes to reach its target from its launch.
The firing of the missile was part of a sharp rise in tensions this week as both Ukraine and Russia have struck each other's territory with increasingly potent weapons.
Russia says that by giving the green light for Ukraine to fire Western missiles deep inside Russia, the US and its allies are entering into direct conflict with Russia.
On Tuesday, Mr Putin approved policy changes that lowered the threshold for Russia to use nuclear weapons in response to an attack with conventional weapons.
Ukrainian President Volodymyr Zelensky said Russia's use of the new missile amounted to "a clear and severe escalation" in the war and called for strong worldwide condemnation.
He said Ukraine was working on developing new types of air defence to counter "new risks".
The Kremlin said the firing of the Oreshnik was a warning to the West against taking further "reckless" actions and decisions in support of Ukraine.
The Oreshnik was fired with conventional, not nuclear warheads. President Putin said it was not a strategic nuclear weapon but its striking power and accuracy meant that its impact would be comparable, "especially when used in a massive group and in combination with other high-precision long-range systems".
He said the missile was incapable of being shot down by an enemy.
"I will add that there is no countermeasure to such a missile, no means of intercepting it, in the world today. And I will emphasise once again that we will continue testing this newest system. It is necessary to establish serial production," he said.
It comes as NATO and Ukrainian officials are due to meet on Tuesday in Brussels to discuss the escalation, diplomatic sources told AFP.
In Kyiv, which is frequently targeted by Russian drones and missiles, parliament cancelled its usual questions today to the government over fears of a strike.
The central area where it is located houses the presidency, the central bank and other government buildings.
It has until now been spared of bombings - unlike the rest of the capital - and access is strictly controlled by the army.
Several MPs said they were working remotely and that today's session had been scrapped.
'Increased risk of attacks'
"There are signals of an increased risk of attacks on the government district in the coming days. Also in Kyiv and Ukraine in general," MP Yevgenia Kravchuk told AFP.
The presidency, however, assured its office was working "as usual in compliance with standard security measures: if the alarm sounds, we will be in shelters."
The apparent heightened risk comes two days after the embassies of several countries, including the US, said they were closed, citing the threat of a Russian attack.
In Moscow meanwhile, Russian defence minister Andrei Belousov said Moscow's advances in the war-battered eastern Ukraine had "accelerated" and also "ground down" Kyiv's best units.
"We have, in fact, derailed the entire 2025 campaign," Defence Minister Andrei Belousov said of the Ukrainian army in a video published by the Russian defence ministry.
Russia later said its forces had "liberated" the frontline village of Novodmytrivka, about 10 kilometres north of Kurakhove, an embattled civilian hub in the eastern Donetsk region that the Kremlin claims is part of Russia.
Observers of the conflict say Moscow and Kyiv racing to gain battlefield advantages ahead of January 2025, when Donald Trump - who has vowed to end the war without saying how - is due to take office in the US.
Mr Belousov spoke a day after Mr Putin had addressed Russians, saying the war in Ukraine, which he launched on 24 February 2024, had taken on "elements of a global character".
Mr Putin said Russia had hit Dnipro with a new type of ballistic missile called the Oreshnik and that Moscow could launch more such missiles depending on "the actions of the United States and its satellites".
The attack, which apparently targeted an aerospace manufacturing plant in the central Ukrainian city of Dnipro, sparked immediate condemnation from Kyiv's allies.
Read more: What is the ICBM Ukraine says Russia fired?
It also shocked residents of Dnipro, which has suffered routine Russian bombardments throughout the invasion.
Vladimir Riga, 66, was on his way to work when he saw "an explosion".
He said the attack damaged a rehabilitation centre and AFP saw workers boarding up the windows of the damaged building after the attack.
Asked if it marked a new turn in the conflict and if he feared an escalation, Mr Riga said, "of course I am afraid. Anything can happen."
The Russian attack also provoked calls for calm from Moscow's allies, including China.
'Terrible escalation'
German Chancellor Olaf Scholz has described Russia's deployment of the medium-range missile as a "terrible escalation".
The Russian attack came after Ukraine recently fired US- and UK-supplied missiles at Russian territory for the first time.
Washington said it had granted Kyiv permission to fire long-range weapons at Russian territory as a response to the Kremlin's deployment of thousands of North Korean troops on Ukraine's border.
Ukrainian President Volodymyr Zelensky has called for a strong response from world leaders to Russia's use of the new missile.
Russian strikes meanwhile killed at least two civilians in the eastern Ukrainian city of Sumy near the border with Russia and one person in the Donetsk region city of Kramatorksk, local authorities said.
