A poster depicting Saad Hariri, who has resigned as Lebanese prime minister, is seen in Beirut on Friday. (Aziz Taher/Reuters)

Secretary of State Rex Tillerson on Friday called on “all parties both within Lebanon and outside” to back off from actions that could threaten that country’s stability, a warning that senior administration officials said was directed at Saudi Arabia as well as at Iran and Hezbollah.

“The United States cautions against any party . . . using Lebanon as a venue for proxy conflicts or in any manner contributing to instability in that country,” Tillerson said in a statement issued by the State Department.

The warning followed several events that have led to growing fear of a war in Lebanon — intended or not — that could engulf the region. Some U.S. and foreign officials worry that strong support for Saudi Arabia by President Trump and presidential son-in-law and adviser Jared Kushner may have helped motivate Riyadh to overplay its hand.

The United States, Saudi Arabia and Israel share concern about expanding Iranian influence in the region. Hezbollah, Iran’s Lebanon-based proxy, now controls significant territory in Syria, near its border with Israel, and in Lebanon. While some Israeli officials have voiced support for moving to constrain Hezbollah, others have urged caution.

Saudi allies such as Egypt have strongly opposed military action against Iran or Hezbollah. “We have to deal with great care so as not to add to the challenges and troubles of the region,” Egyptian President Abdel Fatah al-Sissi told reporters this week. “I am against war.”

Renewed conflict inside Lebanon, where a fragile peace has been maintained for nearly a decade, could endanger the Trump administration’s goal of forging an Israeli-Palestinian settlement and complicate the fight against the Islamic State in Syria and Iraq.

Steps leading to the current crisis began last Saturday, when the Saudis accused Iran and Hezbollah of carrying out an “act of war” with a missile they said was fired at Riyadh by Iranian-backed Houthi rebels in neighboring Yemen.

On the same day, Saudi-backed Lebanese Prime Minister Saad Hariri, who shares power with Hezbollah in an uneasy coalition government, suddenly appeared in the Saudi capital and abruptly announced his resignation from office. The announcement threw Lebanon into confusion and raised fears of war.

On Thursday, Saudi Arabia, Bahrain and Kuwait ordered their citizens out of Lebanon, saying their safety was at risk.

The Saudis have suggested that Hariri was escaping a Hezbollah assassination plot.

In Lebanon, political leaders from differing factions called on Hariri to return and address his political situation from Beirut. His Future Movement political bloc says it does not recognize the resignation.

Hezbollah, which is both a militant group and a political force, has called Hariri’s resignation illegal because it was done from afar. Hezbollah leader Hasan Nasrallah said Friday that the Saudis had kidnapped Hariri and “asked Israel to attack Lebanon.”

On Friday, France also urged Hariri to return and said he must have “all his freedom of movement,” becoming the first Western nation to publicly suggest Hariri is in detention.

Hezbollah has expanded its political role in the complex Lebanese coalition during Hariri’s 11 months in office. The prime minister had been living in exile in Saudi Arabia before his return last year to politics and the job once held by his assassinated father, Rafiq.

Saad Hariri’s abrupt arrival in Saudi Arabia is seen by many in Lebanon as a blunt signal from Riyadh that he had not done enough to rebuff Hezbollah and Iranian influence, and that Saudi Arabia intends to assert its influence in Lebanon against Iran.

U.S. and European diplomats have met with Hariri in Riyadh, but a senior administration official, asked if Hariri was free to leave Saudi Arabia, said, “We don’t know.” In conversations with diplomats, the official said, “there is a question mark as to his ability to speak freely.”

Alongside the Hariri drama, Saudi authorities also announced the arrest last Saturday of more than 200 princes, senior officials and prominent Saudi business executives.

Cast as part of a domestic anti-corruption drive, the arrests also left Saudi Crown Prince Mohammed bin Salman in undisputed control of Saudi security services.That may be an attempt to consolidate power before eventually inheriting the throne.

Trump, traveling in Asia, tweeted strong support for the arrests, saying he had “great confidence in King Salman and the Crown Prince of Saudi Arabia, they know exactly what they are doing.” Since visiting Riyadh in May, the president has repeatedly praised Salman as the leader of the Arab world and a bulwark against Iranian expansion.

Trump has tasked Kushner with leading efforts to forge an Israeli-Palestinian peace, a goal that has eluded U.S. administrations for decades. A major element in Kushner’s strategy is to gather regional Arab support — led by Saudi Arabia — that would bring the Palestinians on board for a potential settlement.

That objective, along with their positions as 30-something scions of powerful fathers, has created a bond between Kushner and Mohammed, who have met privately on a number of occasions this year.

News that Kushner had made an unannounced trip to Saudi Arabia in late October, ahead of Mohammed’s anti-corruption moves and Hariri’s resignation, gave rise to speculation in Washington and in the region that the United States knew about, and approved, subsequent Saudi actions.

A U.S. official said that “if Iran and Hezbollah came up” in discussions between Kushner and Mohammed, “it was brief and in the context of Arab-Israeli peace, and none of these events were touched on.”

Several officials described recent events as evidence that the White House, far from directing or colluding with Saudi policy, has little influence on it. Officials who discussed sensitive relations with Saudi Arabia and the situation in the Middle East spoke on the condition of anonymity.

“I think all of this came as a surprise to everyone,” one official said. “We are deeply concerned about the effects on the stability of Lebanon. That’s why we are speaking as bluntly as we are,” this official said, referring to Tillerson’s statement.

Kareem Fahim in Istanbul contributed to this report.