Russia has a stock of powerful new missiles "ready to be used", President Vladimir Putin has said, a day after his country fired a new ballistic missile at the Ukrainian city of Dnipro.
In an unscheduled TV address, the Russian leader said the Oreshnik missile could not be intercepted and promised to carry out more tests, including in "combat conditions".
Russia's use of the Oreshnik capped a week of escalation in the war that also saw Ukraine fire US and British missiles into Russia for the first time.
Ukrainian President Volodymyr Zelensky called for world leaders to give a "serious response" so that Putin "feels the real consequences of his actions".
His country was asking Western partners for updated air defence systems, he added.
According to news agency Interfax-Ukraine, Kyiv is seeking to obtain the US Terminal High Altitude Area Defense (THAAD), or to upgrade its Patriot anti-ballistic missile defence systems.
In Friday's address Putin said the Oreshnik hypersonic missiles flew at 10 times the speed of sound and ordered them to be put into production. He had earlier said that use of the missile was a response to Ukraine's use of Storm Shadow and Atacms missiles.
Thursday's strike on Dnipro was described as unusual by eyewitnesses and triggered explosions which went on for three hours.
The attack included a strike by a missile so powerful that in the aftermath Ukrainian officials said it resembled an intercontinental ballistic missile (ICBM).
Justin Crump, CEO and founder of the risk advisory company Sibylline, told the OceanNewsUK that Moscow likely used the strike as a warning, noting that the missile - which is faster and more advanced that others in its arsenal - has the capacity to seriously challenge Ukraine's air defences.
This week's escalation has also prompted several warnings from other world leaders about the direction of the war between Russia and Ukraine.
Polish Prime Minister Donald Tusk said the war was entering a decisive stage - with a real risk of global conflict.
Hungarian Prime Minister Viktor Orban meanwhile said the West should take Vladimir Putin's warnings "at face value" because Russia "bases its policies primarily on military power".
And North Korea's leader Kim Jong Un warned "never before" had the threat of a nuclear war been greater and accused the US of having an "aggressive and hostile" policy towards Pyongyang.
North Korea has sent thousands of troops to fight on Russia's side and Ukrainian forces have reported clashes with them in Russia's Kursk region, where Ukrainian troops are occupying some territory.
US President Biden has said he gave Ukraine permission to use longer-range Atacms missiles against targets inside Russia as a response to Moscow's use of North Korean troops.
Russia launched a full-scale invasion of Ukraine in February 2022. Both countries are now trying to secure a battlefield advantage before Donald Trump becomes US president in January.
Trump has vowed to end the war within hours but has not provided details as to how.
In his nightly address, Zelensky also criticised China for its response to Moscow's new missile after China's foreign ministry said all parties should "remain calm and exercise restraint".
"From Russia, this is a mockery of the position of states such as China, states of the Global South, some leaders who call for restraint every time," he said.
He also criticised the Ukrainian parliament for postponing a session on Friday over security concerns following the attack on Dnipro.
In a post on Telegram, he said unless an air raid signal sounded everyone should work as normal - and not take Russian threats as "permission to have a day off".
"The siren sounds - we go to shelter. When there is no siren - we work and serve. There is no other way in war," he said.
