Washington (AFP) - The US military has rescued two Saudi pilots who ejected from their jet off Yemen's coast, as the kingdom launched air strikes on rebel camps in its violence-wracked neighbor, officials said.

The Saudi F-15 fighter jet appeared to be participating in the operations in Yemen, though a US defense official declined to confirm why the men ejected from the plane or why it went down in international waters late Thursday.

The official said Saudi authorities had enlisted Washington's help in the rescue efforts.

During a telephone call, King Salman thanked President Barack Obama for the rescue, the White House said.

"US military assets from USCENTCOM and USAFRICOM recovered the two KSA crew members at approximately 5:20 pm (2120 GMT)" Thursday, the defense official said, indicating the rescue took place at Saudi Arabia's request.

It only took the US military about two hours to rescue the men after being first notified they had ejected from their plane.

The two men, who were rescued by an HH-60 helicopter from Djibouti, were in fit enough a condition to walk, the official added, citing initial reports.

The USS Sterett missile destroyer led the rescue efforts, coordinating assets from the USS New York.

Sunni-ruled Saudi Arabia has vowed to do "whatever it takes" to prevent the fall of Yemen's embattled President Abedrabbo Mansour Hadi, accusing Shiite Iran of "aggression" and backing a months-long rebellion by Shiite fighters.

The spiraling violence has triggered fears that Yemen is becoming the battleground for a regional proxy war along a sectarian divide between Sunnis and Shias.

Obama offered US support for the air strikes led by Saudi Arabia and Gulf allies, saying the United States shared a "collective goal" with the kingdom to see stability in Yemen.

"The president reaffirmed the strong friendship between the United States and Saudi Arabia and emphasized the United States' support for the action taken by Saudi Arabia, Gulf Cooperation Council (GCC) members, and others in response to President Hadi's request and in support of the legitimate government of Yemen," said National Security Council spokeswoman Bernadette Meehan.

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"The president underscored our commitment to Saudi Arabia's security," she added in a statement.

"The president and King Salman agreed that our collective goal is to achieve lasting stability in Yemen through a negotiated political solution facilitated by the United Nations and involving all parties as envisioned in the GCC Initiative."

At least 39 civilians have been killed in Saudi-led Operation Decisive Storm against the Huthis and their allies, officials at the rebel-controlled health ministry in Sanaa said.