Writing in a Financial Times op-ed, the two spy chiefs said "we have no more trusted or esteemed allies" than each other, adding that the partnership would be vital as they "face an unprecedented array of threats", chiefly from Russia, China and in the Middle East.

The ongoing conflict is Gaza is of particular concern, and Burns later told an FT conference in London that he was "working hard" with Egyptian and Qatari mediators to refine a framework for a ceasefire.

"We will make this more detailed proposal, I hope, in the next several days," he added.

The United States and UK are among the leading financial and military supporters of Ukraine in its resistance to the Russian invasion launched in February 2022.

"Staying the course is more vital than ever," they wrote in the op-ed.

"We continue to work together to disrupt the reckless campaign of sabotage across Europe being waged by Russian intelligence."

The pair also explained how they were now using advanced AI and cloud technologies to harness the vast troves of data they collect.

The joint article comes days before UK Prime Minister Keir Starmer's visit to Washington on September 13, where he will be received by US President Joe Biden.

They will discuss, among other things, "continuing robust support to Ukraine" and the desire to achieve a truce in Gaza, the White House said on Friday.

This meeting takes place at a time when the two nations' stance on Israel is diverging.

London has announced the suspension of 30 arms export licences to Israel, citing a risk that they could be used in violation of international law in war-destroyed Gaza.