Saudi Arabia has backed a demand from Yemen's presidential council for the United Arab Emirates to withdraw within 24 hours, after a Saudi-led coalition bombed what it said was a weapons shipment for UAE-backed separatists at the port of Mukalla.

The Saudi foreign ministry accused the UAE of "pressuring" the Southern Transitional Council (STC), which seeks independence for southern Yemen, to launch recent offensives in the eastern provinces of Hadramawt and al-Mahra.

The kingdom would take measures to confront what it considered such "highly dangerous" actions, it warned.

The UAE's foreign ministry denied that the shipment contained weapons and expressed "deep regret" at the Saudi statement.

It strongly condemned "the allegations that it exerted pressure on, or directed, any Yemeni party to carry out military operations that would undermine the security of the sisterly kingdom of Saudi Arabia or target its borders".

The STC's leaders also said the ultimatum for the withdrawal of the UAE's forces had no legal basis, and insisted it would remain a "main partner" in the battle against the Iran-backed Houthi movement, which controls much of north-western Yemen.

Earlier on Monday, the head of the eight-member presidential council - which includes STC representatives - announced that he was cancelling a joint defence pact with the UAE and ordering its forces to leave "in the interest of safeguarding the security of all citizens, affirming commitment to Yemen's unity, sovereignty, stability, and territorial integrity".

Rashad al-Alimi also declared a state of emergency for a period of 90 days, which he said was necessary to confront the Houthis and what he described as "the internal strife led by mutinous military elements that received orders from the United Arab Emirates".

Alimi's announcement came after the spokesman of the Saudi-led coalition - which includes the UAE - said it had carried out a "limited" air strike on weapons and military vehicles for the STC's forces in the southern Yemeni port of Mukalla which arrived on two ships from the UAE.

The shipments had constituted "an imminent threat and an escalation that threatens peace and stability", Maj-Gen Turki al-Maliki asserted.

An official at the port told AFP news agency that a warning to evacuate was received at 04:00 local time (01:00 GMT) and that an open area at the facility was struck about 15 minutes later.

Pictures of the aftermath showed a number of burned out military vehicles and pick-up trucks parked in a walled-off area at the port, as well as damage to a nearby building. No casualties were reported.

The UAE's foreign ministry said it had been surprised by the strike on Mukalla and that the coalition statement had been issued without consultation with member states.

It insisted that the shipment in question "did not include any weapons, and that the vehicles unloaded were not intended for any Yemeni party but were shipped for use by Emirati forces operating in Yemen".

On Saturday, the Saudi-led coalition called on the STC's forces to withdraw "peacefully" from Hadramawt and al-Mahra, a day after the Saudi air force reportedly bombed positions held by the separatists in the Wadi Nahab area of Hadramawt.

The STC's forces launched offensives in the two provinces amid rising tensions earlier this month, putting in direct conflict with government forces.

It said the operations were necessary to "restore stability" in the south and to combat the Houthis, as well as the jihadist groups al-Qaeda and Islamic State (IS).

Yemen has been devastated by a civil war that began in 2014, when the Houthis ousted the internationally recognised government from the capital Sanaa. The conflict escalated in 2015, after the Saudi-led coalition of Arab states intervened to restore the government's rule.

The fighting has reportedly left more than 150,000 people dead and triggered one of the world's worst humanitarian crises.

At the start of the war, the STC and other separatists seeking independence for south Yemen, which was a separate country before unification with the north in 1990, formed an uneasy alliance with the government to stop the Houthis capturing the southern city of Aden.

However, in recent years the STC and its allies have turned on the government and seized control of Aden and much of the south of the country.