Diego Garcia, which is around 2,500 miles (4,000 kilometres) from Iranian territory, is one of 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.

"Iran launched a two-stage intercontinental ballistic missile with a range of 4,000 kilometres toward an American target on Diego Garcia Island," Israeli military chief Lieutenant General Eyal Zamir said in a televised address.

"These missiles are not intended to strike Israel. Their range reaches European capitals -- Berlin, Paris, and Rome are all within direct threat range," Zamir added.

The Wall Street Journal first reported Friday, citing US officials, that Iran launched two ballistic missiles at the base.

While neither 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."

- 'Strategic messaging' -

However, former UK Royal Navy commander and defence expert Tom Sharpe told AFP the long-range missiles may not be a "game changer" in the war.

Iran has "always had missiles of that sort of range that we've known about, maybe not declared", said Sharpe.

The attack "shows that they can still move these mobile launchers around, undetected, spin up and fire without being struck," he added.

"Depending on the weight of the warhead, Iran can increase the range of some of its missiles," explained Ali Vaez, Iran project director at the Crisis Group.

"But this was less about battlefield utility than strategic messaging -- signalling to the United States and Israel that misreading Iran's resolve and capabilities could prove a costly mistake," said Vaez.

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.

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.

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.

burs-aks/pdw