ATACMS missile system during a joint US-South Korean drill in 2017 (Image: Getty)
Outgoing US President Joe Biden has rocked Moscow, after giving President Zelensky the green light to use long-range American-made missiles in Russia.
The move comes after intense lobbying from Kyiv, as well as encouragement from the UK, to allow Ukraine to use the weapons against Putin's forces.
Putin had previously warned that any use of missiles produced in NATO countries would constitute "direct participation" of NATO in the war in Ukraine.
In response to the White House's decision, the Kremlin has accused the Americans of pouring "oil on the fire" of the conflict.
However, the major policy reversal does have one major caveat. Although the ATACMS can reach deep into Russia, Ukrainian forces will not be able to launch them at whatever targets they like.
President Biden and President Zelensky at the G7 Summit in 2023 (Image: Getty)
President Biden has only allowed Kyiv to strike in Kursk - the region of Russia it occupies (Image: Getty)
What are ATACMS missiles?
The MGM-140 Army Tactical Missile System (ATACMS) is a long-range missile system produced by arms giant Lockheed Martin.
The missiles have a range of 190 miles and travel at supersonic speeds. The weapons system has been possessed by the US, Australia, South Korea, Morocco, Romania, Greece, Turkey, Poland, Ukraine and United Arab Emirates.
It was first produced in the 1980s and has been deployed during the Gulf Wars and Iraq Wars. Each ATACMS costs a reported £1.2m.
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Vladimir Putin meets Yevgeny Balitsky, head of the Russian-occupied Zaporizhzhia region of Ukraine (Image: Getty)
Where can Ukraine strike Russia?
The US may have lifted the ban on using ATACMS on Russian targets outside of Ukraine's borders, however that does not mean President Zelensky can order a strike on Moscow.
Firstly, that's because the Russian capital is likely just out of range of the missiles. But beyond that, Washington has placed a limit on where Ukraine can strike Russia using the missiles.
The limit sees Kyiv restricted to protecting Ukrainian positions in Kursk - the region of Russia that it currently occupies. According to the latest live frontline maps, Ukraine's forces retain a presence in Russia - however it only extends a few miles into Russian territory.
Ukraine can use the missiles to defend its positions there, securing its foothold in Russia, but it can't launch strikes into unoccupied Russian land.