Saudi Arabia kept some key details of its military action in Yemen from Washington until the last moment, US officials said, as the kingdom takes a more assertive regional role to compensate for perceived US disengagement.
The Middle East's top oil power told the United States weeks ago it was weighing action in Yemen but only informed Washington of the exact details just before Thursday's unprecedented air strikes against Iran-allied Houthi rebels, the officials said.
US President Barack Obama's Middle East policy increasingly relies on surrogates rather than direct US military involvement. He is training Syrian rebels to take on the government of President Bashar Assad and this week launched air strikes to back up Iraqi forces trying to retain the city of Tikrit.
To Obama's Republican critics, he is ceding the traditional US leadership role. The White House denies it is disengaging from the region and says it has been in close contact with the Saudis over their plans in recent days.
Although the Saudis spoke with top US officials as they debated an air assault in support of embattled Yemeni President Abd-Rabbu Mansour Hadi, US officials acknowledged gaps in their knowledge of the kingdom's battle plans and objectives.
Asked when he was told by Saudi Arabia that it would take military action in Yemen, General Lloyd Austin, the head of the US military's Central Command, told a Senate hearing on Thursday he spoke with Saudi Arabia's chief of defence "right before they took action."
He added that he couldn't assess the likelihood of the campaign succeeding because he didn't know the "specific goals and objectives."
Adel al-Jubeir, Saudi Arabia's ambassador to the United States, said Riyadh consulted closely with Washington on Yemen - but ultimately decided it had to act quickly as Houthi rebels moved toward Hadi's last redoubt in the southern city of Aden.
"The concern was, if Aden falls, then what do you do?" al-Jubeir told a small group of reporters on Thursday. "The concern was that the situation was so dire you had to move."
Saudi Arabia's air strikes point toward an aspiration to defend its regional interests with less reliance on the US security umbrella that has long been the main thrust of Washington's relations with the oil-rich kingdom.