The heads of MI6 and the CIA have accused Russia of conducting a "reckless campaign of sabotage" across Europe.
Sir Richard Moore and Bill Burns said the world is facing “an unprecedented array of threats” and that the global order is under the most severe pressure since the Cold War.
They specifically pointed to Russian President Vladimir Putin's war in Ukraine as a major concern.
China was also singled out as "the principal intelligence and geopolitical challenge of the 21st century," underscoring the complex geopolitical landscape facing Western intelligence agencies.
The pair revealed ongoing efforts by MI6 and the CIA to mitigate the risk of wider conflict in the Middle East, including work towards achieving a ceasefire in Gaza. They also spoke of the "resurgent" threat posed by the Islamic State.
In their joint statement, published in the Financial Times, Sir Richard and Mr Burns wrote: "Today, we cooperate in a contested international system where our two countries face an unprecedented array of threats."
They added: "There is no question that the international world order - the balanced system that has led to relative peace and stability and delivered rising living standards, opportunities and prosperity - is under threat in a way we haven't seen since the Cold War."
The intelligence chiefs highlighted the importance of the UK-US special relationship in addressing these challenges, describing it as built on "Trust, openness, constructive challenge, friendship."
They expressed confidence that "these characteristics can be relied upon into the next century, as can our shared determination to remain champions for global peace and security."
The pair warned about the threat of Russian information operations to Western democracies, citing the Kremlin's"cynical use of technology to spread lies and disinformation designed to drive wedges between us".
Regarding the war in Ukraine, Sir Richard and Mr Burns said: "Staying the course is more vital than ever. Putin will not succeed in extinguishing Ukraine's sovereignty and independence."
They highlighted the impact of technology on the battlefield, stating: "Ukraine has been the first war of its kind tocombine open-source software with cutting-edge battlefield technology, harnessing commercial and military satellite imagery, drone technology, high and low sophistication cyber warfare, social media, open-source intelligence, uncrewed aerial and seaborne vehicles and information operations - as well ashuman and signals intelligence - at such incredible pace and scale.
“Most of all, it has underlined the imperative to adapt, experiment and innovate."
