AL MUKALLA, Yemen – Saudi Arabia on Tuesday declared a UAE-backed separatist advance in Yemen a threat to Riyadh’s national security and called Abu Dhabi’s actions “very dangerous” as the conflict escalated into an open dispute between Gulf powers.

The Foreign Office’s strong statement comes after the Saudi-led coalition fighting in Yemen said it had struck a shipment of arms from the United Arab Emirates destined for separatist forces.

In recent weeks, Abu Dhabi-backed separatists seeking to revive the once-independent state of South Yemen have made considerable territorial gains after launching a blitzkrieg offensive in recent weeks.

Experts say their successes have embarrassed Saudi Arabia, the region’s heavyweight and the main backer of Yemen’s internationally recognized government.

The head of Yemen’s presidential council, which sits atop that government, declared a state of emergency and canceled a security pact with Abu Dhabi after forces of the UAE-backed Southern Transitional Council (STC) seized swaths of territory.

The STC is also part of the government, a motley patchwork of groups held together by its opposition to the Iran-backed Houthi rebels who control swathes of Yemen’s north and west, including the capital Sanaa.

Saudi Arabia and the United Arab Emirates, traditionally close allies who joined forces in Yemen against the Houthis, are increasingly at odds over the conflict unfolding on their doorstep, as well as the war in Sudan.

“The Kingdom (Saudi Arabia) expresses its disappointment with the measures taken by the brotherly United Arab Emirates, pressuring the forces of the Southern Transitional Council to carry out military operations on the southern border of the Kingdom,” the Saudi statement said.

He called them “a threat to the national security of the Kingdom, as well as to the security and stability of the Republic of Yemen and the region.”

“The measures taken by the UAE are considered very dangerous,” he said, adding that “the Kingdom emphasizes that any threat to its national security is a red line, and the Kingdom will not hesitate to take all necessary measures to confront and neutralize such a threat.”

“The fire is still burning”

Riyadh also backed Yemen’s presidential council’s demand that Emirati forces withdraw from the country within 24 hours, and urged Abu Dhabi to suspend its military and financial support for Yemeni groups.

Rashad al-Alimi, head of the Presidential Council, issued decrees on Tuesday announcing a 90-day state of emergency and canceling a security pact with the United Arab Emirates following the separatists’ advance.

Earlier, the Saudi-led coalition said it had targeted a large quantity of weapons and combat vehicles sent by the UAE to secessionist forces.

The coalition struck two ships carrying “a large quantity of weapons and combat vehicles to support the forces of the Southern Transitional Council”, the official Saudi news agency SPA reported.

“Given the danger and escalation posed by these weapons…, coalition air forces this morning conducted a limited military operation targeting the weapons and combat vehicles that had been unloaded from the two ships at the port of al-Mukalla,” the statement said.

The ships arrived from the Emirati port of Fujairah, SPA said, adding that the operation was carried out in accordance with international humanitarian law and without collateral damage.

A port official said an evacuation warning was received at 4 a.m. local time.

“The evacuation was completed and the strike took place a quarter of an hour later in a land area inside the port. The fire is still burning,” the official said on condition of anonymity, not being authorized to speak to the media.

“Unacceptable to God”

Abdullah Bazuhair, whose house overlooks the port, showed AFP the damage to his property, with windows torn from the walls and glass strewn across the ground.

The strikes were “unacceptable in the eyes of God”, he said, adding that “the children were terrified and the women frightened”.

Footage filmed by AFP at the port showed dozens of parked military vehicles and pick-up trucks, several of which were on fire and smoking as workers hosed them down.

The Saudi-led coalition had warned it would support the Yemeni government in any military confrontation with separatist forces and urged them to withdraw “peacefully” from recently seized territories in Hadramawt and Mahra governorates.

Tuesday’s strike came days after Saudi air raids on separatist positions in resource-rich Hadhramaut and after Washington called for restraint in the conflict.

In recent days, hundreds of Yemeni tribesmen gathered in Aden to demand STC leaders announce the independence of South Yemen, according to the independent Aden channel, affiliated with the separatists.

A Yemeni military official said Friday that about 15,000 Saudi-backed fighters were massed near the Saudi border but had not received orders to advance into separatist-held territory.