Russian foreign minister Sergey Lavrov has delivered a chilling warning to Ukraine, after Kyiv used US-made ATACMS missiles in Russia for the first time.

Mr Lavrov said the use of the missiles in the Kursk region of Russia was evidence that Volodymyr Zelensky “wanted to escalate” the war.

He said the Kremlin would “react accordingly”, the Daily Mail reports. Meanwhile, deputy chair of the Russian security council and long-time Putin ally Dmitry Medvedev said the move from Kyiv had signalled “World War III”.

As the conflict entered its 1000th day, Ukraine fired six ATACMS missiles from an unknown location at Russian targets over the border, according to Russia’s Defense Ministry.

The Russian Defense Ministry claimed that at 00:25 GMT Ukraine fired into the Bryansk Oblast. If true, this would contravene reported red lines set out by the US about where ATACMS missiles could be fired on.

According to unconfirmed reports, Washington strictly gave permission for use of the missiles in the Kursk Oblast – a region partially occupied by Ukrainian forces since August.

This comes after Vladimir Putin made a point of updating Russia’s nuclear doctrine, in another thinly veiled threat to NATO powers and Ukraine.

According a report from the Russian state news agency TASS, the Kremlin said it reserves the right “to consider a nuclear response to a conventional weapons attack threatening its sovereignty, a large-scale launch of enemy aircraft, missiles, and drones targeting Russian territory, their crossing of the Russian border, and an attack on its ally Belarus.”

This change of doctrine also gives warning that any conventional missile assault by a state being supported by a nuclear power, could be met by a nuclear response.

The doctrine also stated that any attack on Russia by state in a coalition would be considered an attack by the entire coalition.