Saudi Arabia started its bombing campaign more than two weeks ago, intending to roll back the Houthi-Saleh coalition and help restore Mr. Hadi to power. But that goal has grown increasingly remote. Mr. Hadi has fled the country, the Houthi-Saleh forces have continued to advance, and Al Qaeda’s branch in Yemen has capitalized on the Saudi strikes to extend its own reach.

In Hadhramaut Province around Al Mukalla, the army’s handover of the oil fields to the tribal coalition — essentially for safekeeping — illustrated how the fight is degenerating into a contest among local armed groups filling the void left by the collapse of the Yemeni state.

“We tightened security around the fields and did not allow workers to leave with even a nail,” said Saleh bin Simrat, a spokesman for the coalition, known as the Hadhramaut Tribal Confederacy.

Qaeda fighters have seized the airport, government buildings and a refinery around Al Mukalla, establishing themselves as the most powerful local force. In an effort to win popular support, they have begun calling themselves the Sons of Hadhramaut and have promised to quickly return control of the city to local civilian leaders. When they seized a major army base outside of the city on Friday, they allowed the soldiers inside to leave unharmed, according to a local tribal leader.