U.S. President Joe Biden and British Prime Minister Rishi Sunak on Thursday agreed to deepen close economic ties between the United States and Britain, pledging to accelerate the clean energy transition and strengthen critical mineral supply chains.

The two leaders also discussed their “unwavering support for the people in Ukraine,” Biden told reporters at a joint news conference with the British leader.

Biden and Sunak signed the “Atlantic Declaration,” which Sunak described as a first-of-its-kind economic partnership that mapped out future cooperation on issues such as artificial intelligence, and other economic and commercial relations.

“I know some people have wondered what kind of partner Britain would be after it left the EU,” Sunak said. “I’d say, judge us by our actions. We’re as committed to our values as ever, as reliable of an ally as ever, as attractive an investment destination as ever.”

The two leaders shared laughs and more sober sentiments in the Oval Office about the close relations between prior leaders from the two countries as they previewed topics for the meeting, including AI and Northern Ireland, as well as joint economic and security interests, including in Asia.

The meeting, their fourth in as many months, came as Western officials sought to ascertain whether Russia was responsible for the destruction of the Nova Kakhovka dam, which has displaced thousands of people and caused major economic and environmental damage. Ukraine and Russia have traded blame for the dam’s destruction.

Biden and Sunak fielded questions at the joint news conference after their meeting, an opportunity not afforded to every world leader who visits the White House, and will also issue a joint statement, officials said.

“It’s daunting to think of the conversations that our predecessors had in this room, when they had to speak of wars that they fought together, peace won together,” Sunak told Biden.

“Again, for the first time in over half a century, we face a war on the European continent, and as we’ve done before the U.S. and the UK have stood together to support Ukraine.”

Sunak joked that he would not create the same imposition on Biden that World War Two-era British Prime Minister Winston Churchill did by allegedly wandering around the White House residence in the middle of the night when he was a guest of President Franklin D. Roosevelt.

Sunak brought Biden two gifts, a personalized Barbour jacket and a book written by an ancestor of Biden’s in the 19th century.

Biden and Sunak last met in Hiroshima, Japan, at the Group of Seven summit last month. They also met in Belfast in April and in San Diego in March at a trilateral event marking the defense partnership of the United States, Australia and Britain.

Thursday’s discussion touched on artificial intelligence safety, Sunak told reporters, saying Britain would host the first summit on the issue this autumn to discuss how the risks of AI can be mitigated through internationally coordinated action.

Sunak had pushed to strengthen trading ties between Britain and the United States, keen to show some progress after the Biden administration quashed any speedy prospect of a post-Brexit free trade agreement between the two countries.

In the absence of a bigger trade deal, Britain has cemented deals with individual states and is hoping to reach other such “targeted agreements.”

Sunak was also expected to try to win Biden’s backing for defense minister Ben Wallace’s bid to become the next secretary-general of NATO.

The British leader visited the U.S. Capitol on Wednesday, where he met with Republican and Democratic congressional leaders.

Sunak said on Wednesday a new alliance would help London and Washington protect supply chains and navigate a global economy where new powers are “manipulating global markets, withholding crucial resources and trying to establish a stranglehold over the industries that will define our future.”