Britain should be prepared to review the size of its armed forces given the crisis in the Middle East and the threats from Russia and China, a member of the Biden administration has said during a visit to London. Carlos Del Toro, the US navy secretary, said the UK needed to consider more investment in its navy and reinforcing the army – a day after the head of the British army warned it was too small to fight an all-out war without conscription. Asked specifically about whether the US had concerns that Britain’s armed forces had become too small, Del Toro said: “I think it’s important for the United Kingdom to reassess where they are today, given the threats that exist today.” Although US leaders often call for European countries to increase their defence spending, pointed comments about the UK military are rare because of the closeness of the two countries’ military relationship. The US and UK are engaged in what is likely to be an extended bombing campaign against the Houthis, designed to stop the Yemeni group’s attacks on merchant shipping. However, Del Toro indicated there was no immediate need for Britain to step up its contribution. A shortage of sailors has forced the Royal Navy to decommission two ageing frigates, HMS Westminster and HMS Argyll, reducing its total to nine – while army numbers, at 73,520, are at the lowest level since the period after the end of the war of Spanish succession in 1714. Del Toro said the UK had to make a “decision around whether the army needs to be strengthened” and said that the conflict in the Red Sea demonstrated the need for further spending to protect commercial shipping. “I would argue quite frankly that, given the near-term threats to the UK and the US, then investments in their [the UK’s] navy are significantly important.” That would “ensure that we have this free flow of trade” which “the economy of the United States, allies and partners can mutually benefit from”. Any decision to spend more on the UK armed forces would be a matter for the British government, Del Toro said, but “we in the United States have continued to make significant investments in our national security” amid economic challenges. The US is easily the world’s largest military spender, with a budget of $877bn (£690bn), according to figures compiled by the Economist. Despite recent cuts the UK is the sixth largest in dollar terms, spending £53bn in the current year. Del Toro said he was satisfied with the UK’s naval involvement in the Red Sea. Britain has deployed a frigate, HMS Diamond, which specialises in shooting down drones and missiles. The British were “doing exactly what’s best, which is act as the protective umbrella providing air defence capabilities”. Asked whether the US could widen its operations to attack Iran, which it says provides the Houthis with drones and missile components, and intelligence and surveillance, Del Toro said: “Nothing is off the table.”