Russia is already at war with Nato, a former top commander of the military alliance has said amid transatlantic tensions over Ukraine.
Retired four-star general Curtis Scaparrotti, who also previously led US forces in Europe, warned there was a long-term plan behind the Kremlin's "spurious activities" against member countries and stressed the need to protect critical facilities. One of Moscow's goals was to "break" Nato, he added.
Comments amid strained relations
Mr Scaparrotti's comments at an Atlantic Council think-tank event in Washington, DC, come against a backdrop of strained diplomatic relations after US President Donald Trump struck a diesel supply deal with Russia as he seeks to bring down soaring pump prices ahead of stateside elections next month.
Critics argue the waiving of sanctions on fuel sales by Moscow will only serve to bankroll its war against Ukraine. The ensuing row has led Mr Trump to suggest Ukraine needed a new leader and claim Russian leader Vladimir Putin wanted a peace deal more than the government in Kyiv did.
It has also led to concerns about intelligence sharing by the US and the use of Elon Musk's Starlink satellite communications system, which Ukraine relies on for its defence.
UK support for Ukraine
In a show of support, Andy Burnham hosted Ukrainian leader Volodymyr Zelensky at Downing Street where he pledged continued UK backing. Both leaders also agreed that "Russia had no interest in peace".
The fraught situation comes amid ongoing warnings about the threat posed by the Kremlin to allies of Ukraine, through so-called hybrid warfare, such as drone and cyber attacks. The UK's vital undersea cables have long been seen as vulnerable to sabotage by Russian spy ships.
'We're at war with Russia today'
Referring to "Russian doctrine", Mr Scaparrotti, who served as Nato's Supreme Allied Commander Europe from 2016 to 2019, said: "When they look at warfare, they don't have a line between peace and war.
"Those things that we typically put on the peace side, like these hybrid activities etc, something short of a large physical attack of some kind or one that's done by a conventional force, that's all a part of their spectrum of war, unlike us.
"So that's routine for them, and we've got to come to terms with that.
"So from my perspective, if you looked at it from their spectrum, we're at war with Russia today, within the alliance, because they're taking actions that are intended to undermine individual countries' capability to support warfare, undermine their civilians' confidence in their own government or within Nato, and to break Nato."
He added: "We should take seriously the fact that this isn't just spurious activities on the Russians' part.
"You can count on it that it has a plan behind it, that it's strategic, that it's long-term, and that we should take seriously the protection of our infrastructure."
Trump's approach to Russia
Despite the widely acknowledged threat posed by Moscow, since returning to the White House Mr Trump has taken a conciliatory approach to his Russian counterpart while voicing criticism of traditional allies.
Last month the US president insisted Mr Putin was "not looking to attack Nato territory", despite an attempted drone strike on a German airport that European countries, including the UK, blamed on the Kremlin.
Mr Trump's reticence in condemning Russia has raised further questions over Washington's commitment to the long-standing alliance and its key principle of collective security.
