Russia says Ukraine has fired US-supplied long-range missiles into the country, a day after Washington gave its permission for such attacks.

Ukraine used the Army Tactical Missile System (Atacms) in a strike on Russia's Bryansk region this morning, the ministry of defence in Moscow said.

Five missiles were shot down and one damaged, with its fragments causing a fire at a military facility in the region, it said.

The strike represents the first time the long-range missiles have been used on Russia's internationally-recognised territory after Washington signalled Ukraine had permission to do so. Russia has vowed to "react accordingly.”

On Tuesday, Russia’s foreign minister Sergey Lavrov said Russia would "proceed from the understanding" that the missiles were operated by "American military experts".

"We will be taking this as a renewed face of the western war against Russia and we will react accordingly," he told a press conference at the G20 in Rio de Janeiro.

Moscow said on Monday that any strikes inside its territory with the US missiles would prompt an "appropriate and tangible response".

Ukraine has already been using Atacms in Russian-occupied areas of its own territory for more than a year.

The missiles can hit targets at a range of up to 300km (186 miles) and are difficult to intercept.

Kyiv is now able to strike deeper into Russia using the missiles, including around the Kursk region, where Ukrainian forces hold over 1,000 sq km of territory. Ukrainian and US officials reportedly expect a counter-offensive in the region.

In a statement, Russia’s defence ministry said the strike was launched at 03:25 (00:25 GMT).

A fire caused by fallen debris from one of the missiles was quickly extinguished and there were no casualties, it said.

Ukraine’s military earlier confirmed that it had struck an ammunition warehouse in the Russian region of Bryansk, but it did not specify whether Atacms were used.

It said the attack, on a depot around 100km from the border near the town of Karachev, caused 12 secondary explosions.

Meanwhile, earlier on Tuesday, Putin approved changes to Russia’s nuclear doctrine, setting out new conditions under which the country would consider using its arsenal.

It now says an attack from a non-nuclear state, if backed by a nuclear power, will be treated as a joint assault on Russia.