A Yemeni girl tries out a prosthetic limb at a rehabilitation center in Sanaa in 2016. (Yahya Arhab/EPA/Shutterstock)

Trump administration officials faced tough questions from lawmakers Tuesday over U.S. military support for Persian Gulf nations involved in Yemen, as congressional pressure grows to reconsider the American role in a conflict that has killed thousands of civilians and spawned the world’s worst humanitarian crisis.

Republicans and Democrats pressed representatives from the Pentagon, the State Department and the U.S. Agency for International Development about the implications of U.S. assistance, mostly in the form of arms sales, aerial refueling and intelligence, to a coalition led by Saudi Arabia that is fighting Houthi rebels in Yemen.

The questioning from members of the Senate Foreign Relations Committee indicates growing discomfort with U.S. support for the campaign, which activists say has caused thousands of civilian deaths through reckless airstrikes and exacerbated Yemeni suffering by impeding the import of basic goods.

Robert Karem, assistant secretary for international security affairs, said the United States believed that Saudi Arabia had improved its procedures for conducting airstrikes. A small number of U.S. military personnel are located at a military command center in Riyadh, the Saudi capital, but do not take part in identifying targets for Saudi warplanes.

Karem acknowledged that the Pentagon does not track civilian casualties in Yemen.

“We do not have perfect understanding because we are not using all of our assets to monitor their aircraft” as they conduct operations over Yemen, Karem said. He later suggested that intelligence agencies may track those casualties but did not provide details.

But Sen. Benjamin L. Cardin (D-Md.) said that improved targeting procedures could not be equated with decreased civilian casualties.

A recent report by a United Nations panel of experts found that Saudi Arabia had failed to take adequate precautions as it conducted strikes last year that appeared to target what should have been protected civilian sites. The Trump administration has also faced consistentcriticism from aid groups alleging that U.S. support for Saudi Arabia and its allies has allowed the war to drag on.

“Obviously the proof is in the results, and we don’t know if the results are there or not,” Cardin said. “This is the U.S. reputation that is on the line, and we expect you to know if you report something. . . . Don’t make statements that you can’t back up.”

The hearing comes as a bipartisan group of lawmakers seeks to advance a bill that would subject U.S. assistance to Saudi Arabia to certification on several bench marks, including demonstrable attempts to reduce civilian harm and relieve suffering among Yemenis.

That and other recent actions in Congress indicate a growing willingness to challenge ongoing support for the Saudi-led war.

Although U.S. officials continue to have deep reservations about the conflict, the officials’ defense of current policy reflects the Trump administration’s emphasis on loyalty to Saudi Arabia, its chief Arab ally, and its desire to push back against Iran.

Tehran is thought to be providing military and financial support to the Houthis, who are also Shiite Muslims.

While the Obama administration sought to reduce U.S. support for Saudi Arabia in 2016, the Trump administration has restored some of that assistance.

Some of the most pointed questions came from Democratic lawmakers, but Republican senators also voiced concerns about the conflict’s impact on civilians and the lack of an apparent path toward a political solution.

The United Nations has characterized Yemen as the world’s most dire humanitarian crisis, with millions of people in need of nutrition and millions more suffering from disease, including a major cholera outbreak. Aid agencies say that both the Houthi forces and the Saudi-led coalition are to blame for the suffering.

The Trump administration has asserted that political conditions in Yemen have improved since the death of former Yemeni dictator Ali Abdullah Saleh last year and that the country is ready for renewed attempts to foster peace talks. But lawmakers appeared skeptical.

“And yet we are still sitting here today talking about a peace process blossoming out of a reality on the ground that does not look very different than it did a year or two years ago,” Sen. Chris Murphy (D-Conn.) said.

The lawmakers voiced concerns that the war, which has been grinding on for more than three years, is now poised to get even worse if Gulf forces follow through with an operation to push the Houthis out of Hodeidah, Yemen’s largest port.

David Satterfield, the State Department’s acting assistant secretary for the Middle East, said that the Trump administration had warned the allied governments against taking action that could bring more deprivation and suffering to Yemenis.

“We would not view such an action consistent with our own policy upon which our support is based,” he said.

Sen. Todd C. Young (R-Ind.) pushed Satterfield on whether such an operation, in defiance of U.S. warnings, would prompt a halt or reduction to U.S. support, a commitment the diplomat declined to make.

“So our support would not be conditional on the continued allowance of food, fuel medical supplies and other human assistance into the primary port of Yemen,” Young said with visible frustration.

The hardships facing civilians in Yemen have not been confined to the country’s citizens: migrants from eastern Africa who had fled to Yemen during the war have been tortured, raped and in some cases executed by Yemeni government forces in a detention center in the southern port city of Aden, according to a report released on Tuesday by Human Rights Watch.

The report, based on interviews with former detainees and Yemeni government officials, highlighted growing concerns about lawlessness across the country, even in areas nominally under the control of the Saudi and U.S.-backed government.   The detention facility, which has held hundreds of migrants from Somalia, Ethiopia and Eritrea since 2017 in often squalid conditions, was under the control of the Yemeni government’s interior ministry, according to Human Rights Watch.

Abuse was rampant, the group found. “Former detainees said guards sexually assaulted women, girls, and boys regularly,” the report found. “Boys would be taken at night.” 

Guards beat the detainees with sticks or metal rods, and in some cases, shot and killed detainees. One former detainee told the group that there were “two ways” to leave the facility: “by paying smugglers or by being ‘deported into the sea.’ ”

Correction: An earlier version of this story misidentified Pentagon official Robert Karem. He is the assistant secretary for international security affairs, not the undersecretary for international security affairs.

Kareem Fahim in Istanbul and Karen DeYoung in Washington contributed to this report.