Diego Garcia, which is around 2,500 miles (4,000 kilometres) from Iranian territory, is one of the two bases the UK has allowed the United States to use for "defensive operations" in its war against Iran.

On Friday, the UK government said it would allow Washington to use its bases in Diego Garcia and Fairford in southwest England to target Iranian "missile sites and capabilities being used to attack ships in the Strait of Hormuz".

The UK official source confirmed that Iran's "unsuccessful targeting of Diego Garcia" took place before Friday's announcement.

The source did not confirm additional details about the attack.

The Wall Street Journal reported Friday, citing US officials, that while neither of the two ballistic missiles hit their target the launch suggests that Tehran has missiles with longer ranges than previously thought.

The Pentagon declined to comment.

One of the missiles failed in flight, and the other was targeted by an interceptor fired from a US warship, though it was not clear if the missile was hit, the WSJ reported.

"Iran's reckless attacks, lashing out across the region and holding hostage the Strait of Hormuz, are a threat to British interests and British allies," a UK Ministry of Defence spokesperson said Saturday.

"This government has given permission to the US to use British bases for specific and limited defensive operations."

US President Donald Trump has been critical of UK Prime Minister Keir Starmer's response to the war against Iran, initially refusing to be involved before allowing Washington limited use of the two bases.

American forces have stationed bombers and other equipment at Diego Garcia, a key hub for Asia operations, including the US bombing campaigns in Afghanistan and Iraq.

Trump has also slammed Britain's decision to hand back the Chagos Islands to Mauritius after holding it since the 1960s. Under that agreement, the UK would maintain a lease for the base on Diego Garcia, the largest of the islands.

Iranian Foreign Minister Abbas Araghchi told his UK counterpart Yvette Cooper on a Thursday phone call that any US use of British bases would be considered "participation in aggression", according to Tehran's foreign ministry.

In turn, Cooper warned Araghchi "against targeting UK bases, territory or interests directly", according to a UK foreign office statement.