The UK is “not choosing between the US and the EU”, Prime Minister Sir Keir Starmer has said after President Donald Trump threatened the European Union with trade tariffs.

Over the weekend, Trump announced 25% tariffs on Canada and Mexico – which have both since been paused – and said he would take similar action against the EU but suggested a deal could be “worked out” with the UK.

Asked if he would be willing to water down attempts to forge closer ties with the EU in exchange for keeping the US on side, Sir Keir said both relationships were important to the UK.

“Now, that for me isn’t new, I think that’s always been the case and will be the case for many, many years to come,” he added.

The prime minister told a press conference in Brussels it was “early days” when it came to tariff talks with the US and that he backed “open and strong trading relations”.

Sir Keir was in Belgium to meet Nato Secretary General Mark Rutte and attend talks with EU leaders – the first PM to do so since Brexit.

Asked about tensions between the US and the EU, Rutte said there were “always issues between allies” but that would “not get in the way of our collective determination to keep our deterrent strong”.

On Ukraine, he said Nato – the military alliance of Western countries – had to “not only sustain but continue to step up our support” to ensure Ukraine could negotiate with Russia from “a position of strength”.

He added that spending 2% of national income on defence was “not enough to keep us safe” and that there was “no time to waste” in boosting funding.

Currently Nato asks every member country to spend a least 2% of GDP on defence, however it is thought only 23 of the 32 members meet the target.

Sir Keir said the UK currently spends 2.3% and that his government would shortly be setting out “the path” towards reaching 2.5%.

Speaking at a European Council dinner, the prime minister called for more military collaboration between the UK and Europe including by improving military mobility and logistics across Europe, focusing on research and development and deepening industrial collaboration.

He also said there should be more co-operation to protect against state threats and sabotage, including on subsea infrastructure. This comes after the UK issued a warning to Russia last month after a spy ship was spotted near undersea cables.

While defence is the focus of his Brussels trip, for Sir Keir it is also part of an ongoing bid to “reset” UK-EU relations.

The UK government wants to forge stronger links with the EU – but that could anger the US and risk the UK getting caught up in a trade war.

Similarly, the EU might object to Sir Keir siding with the US rather than its European neighbours.

Earlier, No 10 said the prime minister trusted Trump and pointed to “a really constructive early set of conversations” between the two men.

“We’ve got a fair and balanced trading relationship which benefits both sides of the Atlantic,” the spokesman added.

“It’s worth around £300bn and we are each other’s single largest investors, with £1.2tn invested in each other’s economies.”

Reform UK leader Nigel Farage the prime minister’s commitment to industrial collaboration with the EU showed he was “a rejoiner at heart”.

The UK should be negotiating a free trade deal with the US instead, he told BBC Radio 4’s Today programme on Tuesday, claiming the EU was “diminishing every year”.

“If we start to tie ourselves to industrial collaboration, as it appears was agreed last night, then we find ourselves with less flexibility in doing deals with countries like America.

“My fear is we tie ourselves to EU law.”

Following Trump’s tariffs announcements over the weekend, European and Asian stock markets fell, with car manufacturers particularly badly hit.

The UK was also impacted but to a lesser extent than the EU.

Analysis produced last year by the University of Sussex suggested the UK could face a £22bn hit to exports if the US imposed a blanket 20% tariff on all imports.

Trump believes imposing tariffs will help grow the US economy and protect jobs, however it could lead to consumers paying more as prices adjust to the taxes.

On Monday, Mexican President Claudia Sheinbaum said the imposition of the 25% tariffs had been delayed after reaching an agreement with the US which would see her country deploy 10,000 troops to tackle drug trafficking into the US.

Prime Minister Justin Trudeau also confirmed that Trump’s proposed tariffs of 25% on Canadian goods would be “paused for at least 30 days while we work together”.

European Commission President Ursula von der Leyen said the EU wanted a constructive dialogue with the US but was ready to respond firmly if it was “unfairly” targeted by the new Trump administration.

French President Emmanuel Macron said that if EU interests were attacked, the trading bloc would have to “make itself respected and thus react”.

EU foreign policy chief Kaja Kallas said there were “no winners in trade wars”, but if there was a trade war with the US “then the one laughing on the side is China”.

Asked earlier if he would put tariffs on the UK, Tump said: “UK is out of line but I’m sure that one… I think that one can be worked out.”

He added his discussions with the British prime minister had “been very nice” adding: “We’ve had a couple of meetings. We’ve had numerous phone calls. We’re getting along very well.”

As well as defence the UK wants to discuss easing restrictions on the trade of food and animal products and co-operation on emission trading schemes with the EU.

The mutual recognition of professional qualifications and allowing touring musicians to travel more easily are also areas of interest.

The EU is keen to set up a youth mobility scheme, which would make it easier for young EU citizens to study and work in the UK and vice versa. However, ministers have so far rejected the idea.

Downing Street has not ruled out joining the Pan-Euro-Mediterranean Convention, which would allow tariff-free trade on some goods.

The Conservatives have accused the government of “trying to reopen the divisions of the past and edge us back into the EU”.

In contrast, Liberal Democrat leader Sir Ed Davey has been urging the government to negotiate a new UK-EU customs union, allowing tariff-free trade between the two sides.

Following the tariff announcements, Sir Ed said the US president was “acting like a playground bully” and the UK should “work with our allies in the Commonwealth and Europe to stand strong against Trump”.