Backed by a coalition of Arab allies, Saudi Arabia launched air strikes this week against Shiite Huthi rebels who had been advancing on President Abedrabbo Mansour Hadi's stronghold of Aden in southern Yemen.
Hadi fled to Aden last month after escaping house arrest in the rebel-held capital Sanaa, which the Huthis seized last year.
Supported by the West and Sunni Gulf Arab monarchies, Hadi's government has accused Tehran of backing the rebels in a bid to extend its influence in Yemen.
As the main powers on the opposite sides of Islam's Sunni-Shiite divide, Saudi Arabia and Iran are vying for influence in countries across the region.
But for the Saudis, the possibility of a Tehran-backed Shiite minority seizing control of its southern neighbour was cause for enough concern to move beyond rhetoric and proxies, analysts say.
The intervention was "a last-minute move to prevent Yemen from becoming an Iranian colony," said Antoine Basbous, head of the Paris-based Observatory of Arab Countries.
"The kingdom had no choice but to intervene," said London-based analyst Abdelwahab Badrkhan, adding that the intervention marked a "revival" of Saudi influence among Gulf Arab states, who have increasingly been charting their own path.
Saudi fears of a pro-Iran Yemen are shared by its fellow Sunni Arab nations, in particular Egypt whose air force and navy are taking part in the operation.
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Cairo has even said it is prepared to send troops to take part in the operation, though there has been no indication yet from Saudi Arabia of a ground offensive.
While impoverished and lacking in natural resources, Yemen is strategically located in the southwest of the Arabian Peninsula, along key shipping routes.
The Huthi advance in southern Yemen was threatening not only Aden but the strategic Bab al-Mandab strait, a vital corridor through which much of the world's maritime trade passes.
Nearly 40 percent of global maritime trade is estimated to pass through the strait, much of it on its way to and from the Suez Canal.
Saudi analyst and writer Khaled Batarfi said the kingdom's new ruler -- King Salman, who took over after the death of his brother King Abdullah in January -- had laid the groundwork for the intervention.
"This was the first time that King Salman faced such a challenge and found himself forced to use military force," he said.
But "this was not decided hastily, it was preceded by Arab coordination," he said.
Iran quickly condemned the operation, with President Hassan Rouhani saying: "Interference by foreign militaries is very dangerous and deepens the crisis."
And analysts said it's unlikely Tehran will sit idly by.
Iran will consider the intervention "a challenge to its authority, in which it has invested for decades, not just in Yemen, but in the whole region," Badrkhan said.
"Iran could mobilise groups it could have trained and organised in (Saudi Arabia's Shiite-populated) Eastern Province, or encourage Bahraini opposition to push for violence."