Sir Richard Moore and Bill Burns did not list examples but there has been a spate of mysterious sabotage and arson attacks on infrastructure in the UK, Germany and in the Baltics. Russia is waging a "reckless campaign of sabotage" across Europe, the heads of MI6 and the CIA have warned in their first-ever joint remarks. Sir Richard Moore and Bill Burns also said the UK and the US faced an "unprecedented array of threats", and said the entire world order was under the most serious strain since the Cold War.

In a newspaper article, the spymasters pointed to Vladimir Putin's war in Ukraine, while also describing China as "the principal intelligence and geopolitical challenge of the 21st century".

They touched on the secret work their agencies are doing to try to reduce the chance of wider conflict in the Middle East and revealed that MI6 and the CIA were "working ceaselessly to achieve a ceasefire in Gaza".

In addition, Sir Richard and Mr Burns underlined the "resurgent" danger posed by Islamic State.

"Today, we cooperate in a contested international system where our two countries face an unprecedented array of threats," Sir Richard and Mr Burns wrote in the Financial Times on Saturday.

'The international world order is under threat'

"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," they wrote.

Combatting such risks was at the heart of what the intelligence chiefs described as their two countries' special relationship.

"Trust, openness, constructive challenge, friendship," they wrote. "These characteristics can be relied upon into the next century, as can our shared determination to remain champions for global peace and security."

On Russia, the heads of MI6 and the CIA said Russian intelligence was waging a "reckless campaign of sabotage across Europe".

They did not list examples but there has been a spate of mysterious sabotage and arson attacks on infrastructure in the UK, Germany and in the Baltics.

US intelligence also reportedly foiled an alleged Russian plot to assassinate the chief executive of Germany's leading arms manufacturer.

As well as physical sabotage, Sir Richard and Mr Burns warned of the threat posed to Western democracies by Russian information operations.

'Staying the course is more vital than ever'

They talked about the Kremlin's "cynical use of technology to spread lies and disinformation designed to drive wedges between us".

Turning to Russia's war in Ukraine, the intelligence duo said: "Staying the course is more vital than ever. Putin will not succeed in extinguishing Ukraine's sovereignty and independence."

They said the conflict had demonstrated the impact of technology on the battlefield.

"Ukraine has been the first war of its kind to combine 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 as human and signals intelligence - at such incredible pace and scale. Most of all, it has underlined the imperative to adapt, experiment and innovate."