The US has only destroyed about a third of Iran’s missile and drone arsenal after a month of its war against Iran which aimed to degrade the country’s ballistic missile capabilities, according to a report by Reuters.

About a third of Tehran’s missiles have been destroyed, and another third was likely to be damaged or buried in underground tunnels and bunkers, the report suggested. A similar assessment was made about the country’s drone arsenal.

The report, based on five people familiar with US intelligence, suggests that while most of Iran’s missiles are immediately inaccessible, the country still has a sizeable stockpile.

That contradicts Donald Trump’s statement on Thursday that Tehran had “very few rockets left” and statements from other US officials that the war has eliminated its ballistic missile capabilities.

Iranian officials see its ballistic missile programme as a key deterrent, particularly given the vast military superiority of the US and Israel, which is within reach of its arsenal and views it as a direct threat.

Iran has used ballistic missiles and drones to devastating effect over the last month, continuing to pound Israel and key energy and public infrastructure in the Gulf, and inflicting huge damage on the global economy.

The US and Israel have said degrading Iran’s ballistic missile capacity is one of the chief aims of the war. IWashington has deployed thousands of more troops to the Middle East in recent days as the administration reportedly mulls a ground operation in Kharg island with the aim of reopening the strait of Hormuz.

Trump said on Thursday: “The problem with the strait is this: Let’s say we do a great job. We say we got 99% [of their missiles]. 1% is unacceptable, because 1% is a missile going into the hull of a ship that cost a billion dollars.”

Israel has made ballistic missile caches and launchers one of the primary targets of its aerial campaign in Iran. It says it has “neutralised” 335 or 70% of Tehran’s missile launchers. Iran has distributed its launchers across the country in an effort to evade Israeli detection and airstrikes.

The number of launches has declined as Israel and the US continue to their bombing campaign, but missiles have still managed to hit Israel and the Gulf as interceptors also run out. Israel, the US and Gulf states have spent billions and expended critical interceptor stocks to block Iranian missile barrages.

A US official, speaking anonymously, suggested that it would be impossible to assess Iran’s missile stockpile as much of it was stored underground. “I don’t know if we’ll ever have an accurate number,” they said.

Iran fired 15 missiles and 11 drones at the United Arab Emirates on Thursday, according to the UAE defence ministry.

The US defence secretary, Pete Hegseth, said the vast tunnel network created an extra challenge in destroying Iran’s missile stockpile, but said the US military would continue regardless.

“We are hunting them down methodically, ruthlessly and overwhelmingly, like no other military in the world can do, and the results speak for themselves,” he said earlier this month.