A UK official source told AFP Iran was "unsuccessful" in targeting the Indian Ocean military facility, one of two bases that London has allowed the US to use for certain missions in its war against Iran.

Until now, most had believed Iran -- under US-Israeli bombardment since February 28 -- was unable to strike at such distances, though the feat was unlikely to alter the course of the conflict.

The launch "is a notable development, since the British island used by US forces lies nearly 4,000 km from Iran's coast", researcher Etienne Marcuz of the French Foundation for Strategic Research wrote on X.

That is "beyond the previously estimated maximum range of Iranian missiles", he added.

Previous assessments put Iran's medium-range ballistic missiles (MRBM) at around 3,000 kilometres (1,860 miles).

The CSIS research centre's missile laboratory estimated two MRMBs, the Khorramshahr and Sejjil, to have ranges of 2,000 kilometres, with the former still in development.

The long range of the Diego Garcia shot could be due to a lighter warhead on the Khorramshahr?4, Marcuz noted.

"The lighter the payload, the farther the missile travels," he said.

Other experts, including Ali Vaez of the International Crisis Group, share that view: "Depending on the weight of the warhead, Iran can increase the range of some of its missiles."

- 'Strategic messaging' -

Tom Sharpe of the UK-based RUSI said Iran has "always had missiles of that sort of range", even if they were never acknowledged.

He told AFP the launch shows Iran's military can still "move these mobile launchers around, undetected, spin up and fire without being struck".

For many analysts, the real point wasn't hitting a far-off target but sending a signal.

By demonstrating it can strike at long distances, Iran is trying to restore an image shaken by the heavy bombardment it has faced.

"This is a show of force, a political signal that Iran still has 'secret' capabilities -- at least to the public. But the actual military significance is limited," Marcuz said.

"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," Vaez told AFP.

- Fading restraint -

Israeli analyst Danny Citrinowicz of the INSS said the launch also reflected shifts in Iran's power structure after a series of assassinations of senior leaders.

He called it a "direct result" of the changing balance in Tehran -- notably the rising power of the Revolutionary Guards and the aftermath of the killing of supreme leader Ayatollah Ali Khamenei on the war's first day.

"Despite his deep ideological hostility toward the West, Khamenei exercised a high degree of caution in deploying Iran's capabilities. That restraint is no longer guaranteed," he wrote on X.

"The emerging Iran is likely to behave less like the cautious, calculating actor we've known -- and more like a risk-tolerant, North Korea-style system."

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