A quiet battle for regional influence between Saudi Arabia and the United Arab Emirates burst dramatically into the open last week when Saudi fighter jets bombed Yemen’s port city of Mukalla on Dec. 30, after Riyadh accused Abu Dhabi of sending weapons to separatist rebels in the war-torn country. In an unprecedented move, the kingdom publicly condemned its former ally, saying it was "disappointed" by the UAE’s actions, which it claimed threatened Saudi Arabia’s national security.

The UAE swiftly denied the shipments contained any arms. In an obviously deescalatory move, Abu Dhabi said it would adhere to the ultimatum issued a day earlier by Yemen’s internationally recognized government, which required the UAE to withdraw its forces from the country, where Abu Dhabi backs factions aligned with the Southern Transitional Council (STC) that have fought the Houthis and are now seeking an independent state in southern Yemen. Saudi Arabia opposes a separate state in southern Yemen and sees its potential as a direct challenge to its border security and to the political framework it has invested in since 2015. Yemen was divided into two states from 1967 until unification in 1990. 

Saudi Arabia’s foreign minister, Prince Faisal bin Farhan, is expected to meet with Secretary of State Marco Rubio in Washington on Wednesday, where the situation in Yemen and the rift with the UAE are expected to top the discussion. The Trump administration has sought to maintain neutrality in the row between its key allies, praising both in a Dec. 27 statement for their diplomatic role in Yemen and urging them to exercise restraint and continue to engage in dialogue. Rubio has since held separate phone calls with Prince Faisal and Emirati Foreign Minister Sheikh Abdullah bin Zayed.

The immediate crisis appears to have been contained largely due to the UAE backing down and withdrawing its counterterror force from Yemen. Abu Dhabi officially withdrew from Yemen in 2019 but had a remaining counterterrorism force that it has now pulled out. But the differences that are pitting the Gulf's two most powerful countries against each other are likely only to grow, regional diplomats and analysts say. “The distrust is too deep. The problems are structural and won’t go away,” a senior diplomat serving in the region told Al-Monitor. “This is a fight over the entire Horn of Africa and the Red Sea corridor, a fight over who will be the dominant political and economic force and the main maritime logistics hub in the Middle East,” the diplomat, speaking on background, explained.