WASHINGTON (Reuters) - Despite President Donald Trump’s full-throated support for Saudi Arabia, the United States appears to be signaling a desire for Riyadh to take a more cautious approach in its regional power struggle with Iran, experts say.

Secretary of State Rex Tillerson (L) sits beside U.S. President Donald Trump during a cabinet meeting at the White House in Washington, U.S., November 1, 2017. REUTERS/Kevin Lamarque

The Trump administration, which shares Saudi Arabia’s view of Iran as a regional menace, has strongly backed the Kingdom in the wake of a failed missile attack from Iran-aligned forces in Yemeni territory that demonstrated an ability to strike the Saudi capital.

Trump has cultivated much warmer ties with the Saudis after a fraught relationship with the Obama administration - the president made Riyadh his first stop on his maiden international trip - and has vowed to take strong action to confront Iran. Nevertheless, Washington, which has U.S. forces in Syria and Iraq, is telegraphing a more tempered stance toward the confrontation in a region beset with turmoil.

On Thursday, the State Department called for “unimpeded access” for humanitarian aid to Yemen, after Saudi Arabia imposed a blockade on the country to stem the flow of arms to Iran-aligned Houthi fighters.

A day later, U.S. Secretary of State Rex Tillerson made clear he still recognized as Lebanon’s prime minister Saad al-Hariri, who unexpectedly announced his resignation on Nov. 4 from Riyadh.

In announcing his decision on television, Hariri said he feared assassination and accused Iran and its Lebanese ally Hezbollah of sowing strife in the Arab world, thrusting Lebanon into the front line of the competition between Sunni Saudi Arabia and Shi’ite Iran.

Two U.S. officials said the Saudis, led by Crown Prince Mohammed, had “encouraged” Hariri to leave office and Lebanese officials say he is being held in Saudi Arabia, a charge Riyadh denies. Hariri has not commented publicly on whether he is free to come and go as he pleases.

In a statement on Saturday, the White House said it “rejects any efforts by militias within Lebanon or by any foreign forces to threaten Lebanon’s stability...or use Lebanon as a base from which to threaten others in the region.”

When asked to comment on whether the United States was pushing for a more cautious Saudi response, both the White House and State Department referred to Saturday’s statement on Lebanon.

Tillerson was “not going along with the Saudi position in describing the Lebanese state as under capture by Hezbollah,” said Paul Salem, the senior vice president of the Middle East Institute, a Washington think tank. “That’s significant.”

Tillerson was also “signaling to the Israelis ... that now is not the time to go after Lebanon,” said Salem, referring to long-standing Israeli concerns about Hezbollah’s growing military prowess.

Ray Takeyh, a senior fellow at the Council on Foreign Relations, said he believed the Trump administration was still seeking to help the Saudis advance their interests against Iran without destabilizing the region.

“This is a delicate balancing act. It involves supporting allies in a policy that the administration agrees with, while trying to mitigate aspects of it that it (sees as) overstated,” Takeyh said.

Tillerson’s statement also urged “all parties both within Lebanon and outside” to respect Lebanon’s independence and said there was no role for any foreign forces.

The United States regularly criticizes Iran and Hezbollah for their role in Lebanon. Tillerson’s backing of Hariri and the Lebanese government contrasted sharply with the approach taken by Saudi Arabia, which has lumped Lebanon with Hezbollah as parties hostile to it.

“I see Rex Tillerson as being an old fashioned American diplomat and old fashioned American diplomacy in the Middle East is all about stability,” said F. Gregory Gause, chairman of the International Affairs Department at Texas A&M University.

“I’m not entirely sure that that is the position of the chief executive of the United States,” Gause added.

CONCERNS WITH SAUDI PURGE

The Saudi actions coincide with an anti-corruption purge by the country’s future king that tightened his grip on power.

Trump tweeted on Monday that he had “great confidence in King Salman and the Crown Prince of Saudi Arabia” following the mass arrests - the biggest such purge of the kingdom’s affluent elite in its modern history.

Trump also tweeted that “they know exactly what they are doing.”

Former and current U.S. officials with deep knowledge of Saudi Arabia say Trump’s enthusiastic support for Prince Mohammed has emboldened the youthful Saudi leader.

Tillerson told reporters the purge appeared “well intended” but the mass arrests, which have swept up officials long known in Washington, also fueled U.S. concerns.

“It raises a few concerns until we see more clearly how these particular individuals are dealt with,” Tillerson added.

Trump’s son-in-law, Jared Kushner, the president’s senior adviser, who has cultivated a close relationship with Prince Mohammed, recently returned from Saudi Arabia, fueling speculation on whether he may have had wind of the Crown Prince’s plans. A senior administration official said they had no advance knowledge.