Russia could strike targets in the West if the country is hit with US rockets, the former prime minister has said.
Dmitry Medvedev, now Russian security council deputy chairman, sent the warning after America agreed to provide Ukraine with advanced rocket systems that can strike with precision at long-range Russian targets.
Medvedev told Al Jazeera: "If, God forbid, these weapons are used against Russian territory then our armed forces will have no other choice but to strike decision-making centres.
"Of course, it needs to be understood that the final decision-making centres in this case, unfortunately, are not located on the territory of Kyiv."
US President Joe Biden on Tuesday told reporters that "we're not going to send to Ukraine rocket systems that strike into Russia", a decision Medvedev called "rational."
Biden did not rule out providing any specific weapons but instead appeared to be placing conditions on how they could be used.
On Wednesday, Biden agreed to provide Kyiv with high mobility artillery rocket systems that can accurately hit targets as far away as 80 km (50 miles) as part of a $700 million (£560m) weapons package.
Senior administration officials said that it agreed to provide the arms after Ukraine gave "assurances" that it would not use the missiles to strike inside Russia.
Ukraine had called for the West to send more long-range weapons as it tried to push back Russian troops in the Donbas region.
Watch: Ukraine says it will not launch US weapons into Russia -Blinken
The West has been increasingly willing to give Ukraine longer-range weaponry, including M777 howitzers, as its forces battle Russians with more success than intelligence officials had predicted.
But US intelligence has also warned about growing risks, particularly given a mismatch between Russian president Vladimir Putin's apparent ambitions and the performance of his military.
Medvedev warned the world was getting closer to a nuclear war following the Ukraine invasion.
He added: “The Horsemen of the Apocalypse are already on their way and all hope now is with Lord God the Almighty,’
Thousands of people have been killed in Ukraine and millions more displaced since the Russian invasion on 24 February, which Moscow calls a "special military operation" to "denazify" its neighbour.
Ukraine and its Western allies call this a baseless pretext for a war to seize territory.