The Trump administration is ending the practice of refueling Saudi-coalition aircraft, halting the most tangible and controversial aspect of U.S. support for the kingdom’s three-year war in Yemen, U.S. and Saudi officials said.

The move comes amid escalating criticism of Saudi Arabia’s conduct in the war. Lawmakers from both parties have demanded that the United States suspend weapons sales to Riyadh and cut off aerial refueling of aircraft flown by the Saudi-led coalition, which monitoring groups have accused of killing thousands of unarmed civilians.

Hours after The Washington Post reported a decision had been made, the Saudi and American governments issued statements confirming a halt to the refueling program.

Defense Sec. Jim Mattis said the Pentagon supported the Gulf kingdom’s decision “to use the coalition’s own military capabilities to conduct inflight refueling in support of its operations in Yemen. We are all focused on supporting resolution of the conflict.”

The Saudi Press Agency said the coalition, led by Riyadh and including a number of mostly Arab nations, had “requested cessation” of the refueling due to its own increasing ability.

Analysts said the move would limit Saudi Arabia’s ability to conduct bombing missions.

“This marks the first time that the United States has taken a concrete measure to rein in the Saudi war effort,” said Bruce Riedel, a former CIA officer who is now a scholar at the Brookings Institution. “Two administrations have basically given the Saudis a blank check to do whatever they wanted. Now it will be harder for the Saudis to carry out airstrikes deep into Yemeni territory, going after the capital, for instance.”

[Hundreds of thousands of Yemenis trapped as fighting escalates in strategic port city]

The decision is expected to have a lesser effect on the air operations of the United Arab Emirates, another coalition member whose sorties are flown from just across the Red Sea in Eritrea. The UAE government has said its air operations primarily target al-Qaeda militants rather than Houthi rebels. The coalition launched its operations against the rebels in 2015 because it feared their rise would give Iran a foothold on the Arabian Peninsula.

The announcement comes as Yemeni forces supported by the coalition recently announced a new offensive to capture the Houthi-controlled port city of Hodeida. Aid officials warn that an urban battle there could imperil hundreds of thousands of people.

The U.S.-Saudi relationship has come under closer scrutiny since Saudi Arabia acknowledged that its agents killed Jamal Khashoggi, a prominent Saudi journalist, last month. Democrats, bolstered by a string of midterm election victories in the House, have also called for greater oversight of the war.

Though U.S. military officials have continued to publicly defend the Saudi-led coalition’s efforts to avert civilian casualties, privately they have expressed a feeling of being stuck between a rock and a hard place. U.S. military leaders, many of whom have years of experience working closely with Persian Gulf allies, see Saudi Arabia as a key partner in the counterterrorism fight that has dominated Pentagon operations since 2001. They also share Riyadh’s concern about Iran’s reach through proxy forces and want to show support for the kingdom as it grapples with repeated missile and other attacks from the Houthi rebels.

But the officials are also frustrated that they are blamed for atrocities in a conflict in which they believe they have a minor supporting role and which they often have little ability to shape. U.S. air tanker activity represents only about a fifth of overall refueling activity for the coalition’s campaign over Yemen, according to the Defense Department.

The decision to halt refueling occurs as the Trump administration seeks to throw its support behind efforts by the U.N. envoy for Yemen, Martin Griffiths, to initiate discussions that might lead to a peace deal. Griffiths had hoped to bring the Houthis together with representatives of Yemen’s internationally recognized government this month but, in an acknowledgment of the challenge negotiators will face, he now hopes to do so by the end of the year, U.N. officials said Thursday.

Critics say the Trump administration’s attempt to foster a peace process is undermined by its failure to exert adequate pressure on Saudi Arabia.

“The United States has the clout to bring an end to the conflict — but it has decided to protect a corrupt ally,” Mohammed Ali al-Houthi, a senior Houthi official, said in an opinion article in The Washington Post.

On Friday, Sens. Todd C. Young (R-Ind.) and Jeanne Shaheen (D-N.H.) renewed their calls for a suspension of U.S. refueling in a war that has killed at least 10,000 people. “We must send an unambiguous, immediate, and tangible message that we expect Riyadh to engage in good faith and urgent negotiations to end the civil war,” the lawmakers said in a statement. “Riyadh must also understand that we will not tolerate the continued indiscriminate airstrikes against civilians and civilian infrastructure that have helped put 14 million Yemenis on the verge of starvation.”

U.S. military officials have said their refueling program seeks to enable defensive missions conducted by coalition planes — targeting a Houthi site, for example, from which a missile is thought to have been launched into Saudi Arabia — but acknowledge that they do not track what occurs once those planes have been refueled. In March, Army Gen. Joseph Votel, head of U.S. Central Command, told Sen. Elizabeth Warren (D-Mass.) that U.S. forces did not track whether U.S. fuel or munitions had been used in coalition operations that resulted in civilian deaths.

Warren condemned the actions of Iranian-linked forces in Yemen but said the United States must insist on accountability from Saudi Arabia, because it provides the kingdom with aid. “That means we bear some responsibility here, and that means we need to hold our partners and our allies responsible for how those resources are used,” she said.

In the past, military leaders have argued that ending aerial refueling could have a dangerous effect. This spring, Defense Secretary Jim Mattis said in a letter to lawmakers that legislation seeking to force an end to military support “could increase civilian casualties, jeopardize cooperation with our partners on counterterrorism and reduce our influence with the Saudis — all of which would further exacerbate the situation and humanitarian crisis.”

The Trump administration also shares intelligence with coalition forces and has continued to support massive arms sales, including precision-guided munitions that U.S. officials have argued enable the coalition to conduct more-precise air operations. U.S.-manufactured munitions have been found repeatedly at the sites of strikes on Yemeni civilians.

U.S. military officials say Saudi Arabia has taken steps to improve its air operation, particularly after an Aug. 9 strike that killed more than 40 Yemeni children.

During the final years of the Obama administration, the U.S. military had a more substantial footprint in the coalition air command center in Saudi Arabia. But it reduced the number of personnel there after a temporary cease-fire in 2016 and since then has sought to maintain its distance from the coalition’s targeting operations.

The move to end more than three years of refueling may not satisfy critics in Congress, who would like to see broader action to curtail U.S. involvement in the war. The U.S. military conducts a separate campaign in Yemen along with Emirati forces against al-Qaeda in the Arabian Peninsula. It wasn’t immediately clear whether that operation would be affected by the decision.

Sen. Chris Murphy (D-Conn.), a prominent critic of U.S. involvement in the war, said Friday’s decision amounted to an admission that the Yemen campaign had been a failure.

“Now that it’s no longer a secret that the war in Yemen is a national security and humanitarian nightmare, we need to get all the way out ,” he said in a statement.

Karen DeYoung contributed to this report.