The coalition had warned it would back Yemen's government in any military confrontation with separatist forces and has urged them to withdraw "peacefully" from recently-seized provinces.

In recent weeks the UAE-backed Southern Transitional Council (STC), which seeks to revive the formerly independent state of South Yemen, has swept through swathes of the country, expelling other government forces and their allies.

These advances have put pressure on ties between Saudi Arabia and the UAE, which support rival groups within Yemen's government.

"The crews of the two ships disabled their tracking systems and unloaded a large quantity of weapons and combat vehicles to support the Southern Transitional Council forces," Saudi state news agency SPA reported.

"Given the danger and escalation posed by these weapons... the Coalition air forces carried out a limited military operation this morning targeting weapons and combat vehicles that had been unloaded from the two ships at the port of al-Mukalla."

The ships arrived from the port of Fujairah, on the east coast of the United Arab Emirates, SPA said, adding that the operation was conducted in accordance with international humanitarian law and that no collateral damage occurred.

-'Sensitive moment'-

The attack came days after reported Saudi air strikes on separatist positions in Yemen's Hadramawt province -- and after Washington called for restraint in the rapidly escalating conflict.

US Secretary of State Marco Rubio said: "We urge restraint and continued diplomacy, with a view to reaching a lasting solution."

Saudi Defence Minister Khalid bin Salman posted on X that troops from the separatist STC should "peacefully hand over" two regional governorates to the government.

"It's time," he posted, "at this sensitive moment, to let reason prevail by withdrawing from the two provinces and doing so peacefully."

But the STC warned on Friday that they were undeterred after strikes blamed on Saudi Arabia hit their positions, in the latest escalation since they seized large swathes of territory in the Hadramawt and Mahrah provinces.

Since the takeover, supporters of the separatists have been gathering regularly in cities including Aden to demand they declare independence, with the largest rallies taking place every Friday.

On Saturday, hundreds of Yemeni tribesmen gathered in Aden to ask the STC's leaders to announce the independence of South Yemen, according to the separatist-affiliated Aden Independent Channel.

The channel aired footage of a large crowd marching and waving the South Yemen independence flag alongside the UAE's flag.

A Yemeni military official said on Friday that around 15,000 Saudi-backed fighters were amassed near the Saudi border but had not been given orders to advance on separatist-held territory.

The areas where they were deployed are located at the edges of territory seized in recent weeks by the UAE-backed STC.

The government is a patchwork of groups that includes the separatists, and is held together by shared opposition to the Iran-backed Houthis.

The Houthis pushed the government out of Yemen's capital Sanaa in 2014 and secured control over most of the north.