Russia is preparing to launch cyber attacks against critical British infrastructure in response to UK air strikes on Syria last Friday.
In a joint statement, the British National Cyber Security Centre (NCSC), the FBI, and the US Department of Homeland Security warned that a global hacking campaign by the Kremlin had already started.
The threat alert said that attackers were trying to hack into computer networks at government and private sector organisations, as well as internet service providers.
It explained that hackers were trying to gain access to the networks for espionage, as Russia laid "a foundation for future offensive operations."
Ciaran Martin, head of the NCSC, said Russia was: "our most capable hostile adversary in cyber-space, so dealing with their attacks is a major priority for the National Cyber Security Centre and our US allies."
This is the first time that in attributing a cyberattack to Russia, the US and the UK have, at the same time, issued joint advice to industry about how to manage the risks from attacks
It marks an important step in our fightback against state-sponsored aggression in cyberspace
According to Martin, many of the techniques used by Russia, "exploit basic weaknesses in network systems."
The NCSC boss also said the centre was leading the way to "issue advice and automate defences at scale to remove those basic attacks, thereby allowing us to focus on the most potent threats."
"The UK government will continue to work with the US, other international allies and industry partners to expose Russias unacceptable cyber behaviour, so they are held accountable for their actions," he commented.
Fears that a Russian attack could be imminent were voiced over the weekend by cabinet minister Boris Johnson, who warned the UK needed to take "every precaution" to defend itself from a potential attack.
Russia's attack follows air strikes made by US, UK and French forces on Friday night in response to a suspected chemical weapons attack by the Assad regime in Syria.