Saudi Arabia told the Obama administration and Persian Gulf allies early this week that it was preparing a military operation in neighboring Yemen, and relied heavily on U.S. surveillance ­images and targeting information to carry it out, according to senior American and Persian Gulf officials.

Despite days of planning for possible airstrikes, officials said, the Saudis withheld a final decision until it became clear late Wednesday that Houthi rebels were poised to take over Aden, the country’s main southern port.

The capture of Aden, the Saudis believed, would eliminate any chance for an early end to the fracturing of Yemen. Retaining control of the city was seen as crucial to reinstalling the government of President Abed Rabbo Mansour Hadi, who secretly fled Aden on Wednesday.

Within hours, acting on orders from King Salman, the Saudis notified allies already signed up for the operation, including the United States, that it was a go. The first airstrikes began at 2 a.m. Thursday, Yemen time.

Officials declined to speculate on how long the operation might last but said the hope was that the air action would persuade the Houthis to enter into political talks they have resisted since their sweep through the country began last summer.

A ground war across Yemen’s barren mountains and deserts was described by the officials, some of whom spoke on the condition of anonymity, as both unanticipated and unlikely, even as the Saudis have massed forces along the Yemeni border and Egyptian warships were said to be steaming down the Red Sea. The officials, however, did not rule out the use of ground troops to help protect Hadi and his government, assuming he can be returned to Aden. Hadi, who fled first to Oman, arrived Thursday afternoon in Riyadh, the Saudi capital.

As the air campaign moved into its second day, other countries from the region and beyond were expected to begin flying missions alongside the Saudis. Adel al-Jubeir, Saudi Arabia’s ambassador to Washington, said that “the first wave went extremely well” with “no collateral damage that we know of.”

Only Saudi aircraft participated in the initial strikes, Jubeir said, many of which were directed at destroying sophisticated weapons and aircraft the rebels have seized from overrun Yemeni government facilities in and around Sanaa, the capital.

U.S. and Saudi officials reacted sharply to allegations by senior Republican lawmakers that the Saudis had purposefully left the United States out of the loop until the last minute because they no longer trusted an administration too eager to stay on the good side of Iran. The United States and other global powers are in the final days of tense negotiations with Iran over a deal designed to prevent that country from developing nuclear weapons.

Shiite Iran — locked with Sunni Saudi Arabia in a regionwide struggle for dominance, one with strong sectarian overtones — is said to have aided the Houthis with weapons, financial support and military advice.

“I think it’s fine that they did it themselves, but the question is, what’s the reason for it?” Sen. John McCain (R-Ariz.), chairman of the Armed Services Committee, said of the Saudi-led Yemen operation.

He continued: “And the reason is, they’ve stated publicly that they can no longer rely on the United States of America. And it is also, in our view as well as theirs,” he said of the Saudis, “unacceptable that we are negotiating a bad nuclear deal and at the same time turning a blind eye to Iranian aggression, whether it be in Lebanon, in Damascus, in Baghdad or now in Sanaa.”

Thousands of angry Houthis rallied in the Yemen capital of Sanaa on Thursday to protest airstrikes on Houthi rebels by Saudi Arabia and its allies. (Reuters)

Earlier, House Speaker John A. Boehner (R-Ohio) said the administration had “no strategy” and was “sitting on the sidelines.”

Jubeir, while agreeing that his government has repeatedly expressed its “concerns” about Iran to the administration, said that no one should “underestimate the strength and depth of relations between the United States and Saudi Arabia. It has been tested on many occasions and surprised many people.”

“When push comes to shove, this relationship is unshakable,” he said.

Saudi and U.S. officials described the potential benefits of a Saudi-led operation as beyond simply the hoped-for result of bringing the Houthis to heel.

Airstrikes led by regional Sunni powers are seen as key in persuading Yemen’s Sunnis from joining forces with al-Qaeda’s franchise in that country to fight against the Shiite Houthis. This franchise is known as al-Qaeda in the Arabian Peninsula.

“What we want to be wary of, and one reason why the Saudi intervention is positive, is we don’t want AQAP to try to establish itself as the vanguard of Sunni opposition to the Houthis,” a senior administration official said, speaking on the condition of anonymity because of the sensitivity of the matter.

At the same time, intelligence assistance and strong statements of support for the operation would prove to Persian Gulf allies that the administration is clearly willing to disregard its negotiations with Iran and “put skin in the game.”

The administration realizes, the official said, that any U.S. relationship with Iran “may only serve to heighten Saudi sensitivity” to the threat that a well-armed Iranian-backed Houthi force in Yemen poses to the kingdom. But “we’ve shown that when it comes to the security” of the Persian Gulf countries, “we have their back, providing them with unique and indispensable capabilities to facilitate their actions.”

According to a timeline provided by U.S. and Saudi officials, discussions about possible military intervention in Yemen began last summer as Houthi rebels moved southward from their traditional homeland, along the Saudi border in northern Yemen. By September, although there was little concern that they were capable of ousting the government, the rebels had moved into Sanaa and formed a fragile power-sharing arrangement with Hadi’s government.

During a strained fall and winter, it became clear the Houthis were allied with former Yemeni president Ali Abdullah Saleh, who had resigned in early 2012 under pressure from the Saudis and other Persian Gulf neighbors. The Houthis agreed to numerous offers of negotiation from Hadi’s government and the Gulf Cooperation Council — which includes Saudi Arabia, Kuwait, Bahrain, Qatar, Oman and the United Arab Emirates — only to then reject them or ignore agreements that were made.

As violence grew in the capital, the United States and other countries shuttered their embassies. Last month, Hadi, a prisoner in his own home, escaped to Aden and declared it Yemen’s temporary capital.

It was only last weekend, however, that the Saudi plans moved into high gear following a defiant Hadi speech that was answered by a Houthi call to arms. Assisted by military units loyal to Saleh, the Houthis began to move toward Aden.

On Monday, the Saudis began to call in chits already offered by allies. As Persian Gulf neighbors flew attack planes to bases in southern Saudi Arabia, Saudi intelligence and military officials met with U.S. officials to identify targets. A joint Saudi-U.S. cell was established in Riyadh to share real-time information from U.S. intelligence assets over Yemen.

Rather than asking for direct U.S. military participation, the Saudis were “focused on . . . the type of additional resources and intelligence that we could render,” the senior administration official said.

“This was all finalized yesterday,” the official said. But “we certainly knew heading into yesterday.”

Mike Debonis contributed to this report.