The international world order is “under threat in a way we haven’t seen since the Cold War”, the heads of the UK and US foreign intelligence services have warned.

The chiefs of MI6 and the CIA also said both countries stand together in “resisting an assertive Russia and Putin’s war of aggression in Ukraine”.

In a first-ever joint article, Sir Richard Moore and William Burns wrote in the Financial Times that they saw the war in Ukraine coming “and were able to warn the international community”, in part by declassifying secrets to help Kyiv.

And they said there was work being done to “disrupt the reckless campaign of sabotage” across Europe by Russia, push for de-escalation in the Israel-Gaza war, and counterterrorism to thwart the resurgent Islamic State (IS).

The pair also made their first public speaking appearance together at a security summit in London on Saturday.

In the FT op-ed, they wrote: “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.”

“Successfully combating this risk” is at the foundation of the special relationship between the UK and US, they added.

One of the “unprecedented array of threats” faced by both countries is the war in Ukraine, which is in its third year after Russia’s invasion in February 2022.

Sir Richard and Mr Burns said “staying the course is more vital than ever” when it comes to supporting Ukraine, adding Russian President Vladimir Putin “will not succeed”.

They continued: “Beyond Ukraine, we continue to work together to disrupt the reckless campaign of sabotage across Europe being waged by Russian intelligence, and its cynical use of technology to spread lies and disinformation designed to drive wedges between us.”

Both foreign intelligence services see the rise of China as the main intelligence and geopolitical challenge of the century. They have reorganised their services “to reflect that priority”, they added.

The pair also said they have pushed “hard” for restraint and de-escalation in the Middle East, and have been working “ceaselessly” to secure a ceasefire and hostage deal.

It is 11 months since Hamas attacked southern Israel on 7 October, killing about 1,200 people and taking another 251 hostage.

More than 40,000 people have been killed in Gaza since then in Israel’s ongoing military campaign, according to the territory’s Hamas-run health ministry.