The gathering comes amid the conflict in Ukraine and the Israel-Hamas war.
Terrorism “must not prevail” in Ukraine or Israel, Rishi Sunak has told a summit of northern European nations in Sweden.
The Prime Minister is on the Baltic island of Gotland for a UK-led defence grouping, where the war in Ukraine and the escalating crisis in Israel and Gaza will top the agenda.
The 10-strong Joint Expeditionary Force gathering had been expected to see the leaders focus on the threat from Russia as the war in Ukraine heads into another winter.
The invasion has focused minds in northern European about the threat posed by Vladimir Putin, with a fresh emphasis placed on security co-operation in the region.
While security and support for Ukraine is still set to dominate discussions, with Ukrainian President Volodymyr Zelensky addressing leaders on Friday, the conflict raging in the Middle East has overshadowed the meeting.
The Prime Minister, who spent Thursday night aboard a Royal Navy frigate in Gotland, opened his address to fellow leaders with a pledge to support both Ukraine and Israel.
“I think it’s important for us to say that we’re all outraged by the terrorist attacks that have happened in Israel.
“As you will all agree that we will stand with Israel at this moment. I’ve offered Prime Minister Netanyahu my full support.
“Terrorism will not, must not, prevail, in Ukraine, in Europe, in anywhere else.”
Ahead of the summit, Mr Sunak met with Swedish Prime Minister Ulf Kristersson aboard HMS Diamond, something the British leader described as a “symbol” of the co-operation between the two countries.
The two men will sign a new strategic partnership agreement as part of the gathering.
Downing Street said the pair discussed “shared European challenges such as energy security and illegal migration”, while also agreeing on the need to keep backing Kyiv as the war continues.
The Prime Minister described the Joint Expeditionary Force as the “first line of defence”, as he praised progress on defence co-operation.
“We’ve done more in the last 18 months than we’ve done in almost a decade before,” he said. “I think that speaks to the energy which we put into this gathering but also the urgency that the situation demands.”
Ahead of his arrival in Sweden, the Prime Minister confirmed the UK will send Royal Navy vessels and surveillance aircraft to the eastern Mediterranean to support Israel.
Mr Sunak said the deployment will “support efforts to ensure regional stability and prevent further escalation”.