Keir Starmer has joined Emmanuel Macron in Paris for the French Armistice Day service, in a pointed show of European solidarity days after Donald Trump’s re-election, with Ukraine and defence on the agenda for private talks between the two leaders.

Starmer became the first UK leader to attend France’s national commemoration event since Winston Churchill in 1944.

No 10 and the Élysée are said to be hoping the meeting will be a significant European moment for France and the UK, two leading Nato powers, amid fears on the continent about the future of the alliance after Trump’s re-election.

The prime minister flew to Paris early on Monday to attend the event with French and British veterans. He also had a breakfast reception with representatives of the British defence community in France.

A spokesperson for No 10 said Starmer and Macron discussed how to put Ukraine in a strong position.

“The leaders started by discussing the situation in Ukraine, including how best to put Ukraine in the strongest possible position going into the winter,” they said.

“Turning to the Middle East, both underscored their deep concern at the situation in Gaza and Lebanon. They also reiterated the need for stability in the West Bank.

“Reflecting on the situation in the Channel, the prime minister set out his mission to disrupt and deter smuggling gangs across Europe, and the leaders strongly agreed on the importance of bearing down on illegal migration at every stage of a migrant’s journey.”

Whitehall officials have been tasked with examining how Trump’s victory will affect the final shape of the strategic defence review (SDR) due to be reported in the spring. Starmer and the chancellor, Rachel Reeves, are understood to be planning to set out a path before that deadline on how the UK can reach the 2.5% of GDP defence spending target for Nato member states.

Starmer and the foreign secretary, David Lammy, have cited the defence target as an area of common ground with Trump, who has repeatedly called for Nato countries to provide more funds and to reduce their reliance on US spending.

Trump has previously urged Nato allies to spend 3%, a marked increase from the current UK level. Speaking at a campaign in August, he said: “I’ll insist that every Nato nation must spend at least 3%. You have to go up to 3% – 2% is the steal of the century, especially as we’re paying for it.”

During the US election campaign, he said he would find a solution to end Vladimir Putin’s war in Ukraine “within a day”, but did not explain how he would do so. His vice-presidential nominee, JD Vance, has been vociferously opposed to providing more funds to support Ukraine.

The Wall Street Journal reported that among Trump’s plans to bring about an end to the conflict was the establishment of an 800-mile demilitarised zone between the Russian and Ukrainian armies, policed by European troops.

Bryan Lanza, a political adviser to Trump since his 2016 presidential campaign, suggested on the BBC this weekend that Trump would force territorial concessions from Ukraine.

“When [Volodymyr] Zelenskyy says we will only stop this fighting, there will only be peace, once Crimea is returned, we’ve got news for President Zelenskyy: Crimea is gone.” But a spokesperson for Trump’s presidential transition team said later on Saturday that Lanza had not been speaking on behalf of the president-elect.

On Sunday, a UK cabinet minister said the government was examining all possible options in terms of a potential change of approach to Ukraine by the US.

Whitehall officials were “considering and planning lots of different scenarios”, Darren Jones told Sky News on Sunday. Jones said the UK would not be stepping back from its own commitments. “We don’t want any countenance of the idea that we’re stepping back from that. That’s why we’re offering them £3bn a year, which you know, in the fiscal context here in the UK, is difficult but the right decision for us,” he said.

“Officials will be considering and planning lots of different scenarios – as they would do under any administration – to make sure that the UK is in the strongest possible position.”

However, Jones said he would not specifically commit to spending 2.5% of GDP on defence by the end of the current parliament, saying security and defence were a priority but that meant “trade-offs” in other areas.

Military experts have said the incoming Trump administration has given new impetus to the need for Nato allies to “mend fences”.

Dr Karin von Hippel, the director of the Royal United Services Institute thinktank, said it was a symbolic moment to have the French president and Starmer stand united.

“It’s important for the United Kingdom and the EU to mend fences and forge a stronger relationship now that Trump has won. The same applies to UK bilateral relations with European countries.

“America will no longer be a reliable partner for any European country, including the UK. So as much bridge building and scenario planning that can be done now is critical, including deciding where they will push back on the United States when they disagree.”

In Paris on Monday, Starmer will also meet the new French prime minister, Michel Barnier, the former Brexit negotiator whom Starmer met several times as shadow Brexit secretary.

Starmer said: “I am honoured to be in Paris to stand united with President Macron in tribute to the fallen of the first world war who made the ultimate sacrifice for the freedom we enjoy today.

“These events are vital in ensuring the memory of millions of young soldiers, sailors and aviators live on for generations to come.”

Announcing the visit, Starmer promised £10m of government funds for the 80th anniversaries of VE Day and VJ Day on 8 May and 15 August next year, promising events to involve tens of thousands of military personnel.

The prime minister has repeatedly said the UK’s commitment to Ukraine would be “ironclad” no matter the US president’s approach, although officials in Kyiv have told the Guardian they are frustrated over Britain’s failure to supply additional long-range missiles.

On Sunday, the UK’s chief of the defence staff said approximately 1,500 Russian troops were being killed and injured every day. Adm Sir Tony Radakin said Russia was still paying an “extraordinary price” for Putin’s invasion and October was the worst month for losses since the conflict began in February 2022.