WASHINGTON—U.S. lawmakers from both parties are challenging the Trump administration’s support for Gulf allies battling Iran-aligned fighters in Yemen, putting new pressure on the U.S. president to scale back ties with Saudi Arabia during an especially sensitive time.
A bipartisan group of senators plan to demand answers on Wednesday from Secretary of State Mike Pompeo after he backed Saudi Arabia and the United Arab Emirates over the objections of most of his Yemen experts.
In a letter expected to be delivered to Mr. Pompeo on Wednesday, the lawmakers, including Sens. Susan Collins (R., Maine), Chris Murphy (D., Conn.), and Todd Young (R., Ind.), write that they have “significant concerns” with his support for the Gulf allies.
“We find it difficult to reconcile known facts” with the decision to officially certify that Saudi Arabia and the United Arab Emirates were taking meaningful steps to minimize civilian casualties in Yemen and that they were following the law when using weapons sold by the U.S. The certification was the first by Mr. Pompeo under a new law that requires him to certify to Congress every six months that the Gulf nations are doing all they can to minimize civilian casualties in Yemen.
State Department officials didn’t immediately respond to requests for comment.
The letter is part of an expanding effort in Congress to choke off American support for the two Gulf allies trying to contain a threat posed by Houthi fighters. The Saudi-led coalition has been trying to reinstall the head of the internationally recognized government, forced into exile when Houthi fighters seized Yemen’s capital in 2015.
The stepped-up pressure from Congress comes as Saudi Arabia is facing scrutiny over the disappearance of a prominent Saudi critic. Numerous U.S. lawmakers are demanding answers about the well-being of Jamal Khashoggi, a well-known Saudi writer who disappeared after going to the Saudi consulate in Istanbul to pick up papers needed to get married.
Turkish officials have said that Mr. Khashoggi was killed by a special hit team sent to Istanbul to silence a dissident. Saudi officials have denied the allegation and said that Mr. Khashoggi left the consulate and disappeared.
No one has publicly produced evidence to show definitively that Mr. Khashoggi is dead or alive. But the possibility that Mr. Khashoggi may have been killed by Saudi Arabia has stoked alarm in Congress, where lawmakers are already discussing ways to cut off aid.
One of the major administration fears is that the civilian casualty concerns in Yemen will compel enough U.S. lawmakers to support proposals to cut off military aid to the Saudi-led coalition.
The U.S. currently provides Saudi Arabia and the United Arab Emirates with modest military support, including aerial refueling of jet fighters carrying out airstrikes in Yemen, limited battlefield intelligence, and billions of dollars in weapons. The three nations work closely together in a parallel fight against al Qaeda and Islamic State militants who are using lawless sections of Yemen as sanctuary.
Saudi Arabia and the U.A.E. have been unable to extricate themselves from the war in Yemen, the location of what the U.N. calls the world’s worst humanitarian crisis. Houthi fighters in Yemen are increasingly using Iranian-made missiles to target neighboring Saudi Arabia. And the Trump administration views the war in Yemen as a strategic battleground in its push to contain Iran’s regional influence.
Over the past three years, according to the U.N., the Saudi-led coalition has killed thousands of civilians in Yemen, most of them in airstrikes that have fueled concern in Washington.
Those worries peaked in August when a coalition airstrike attacked a school bus in Yemen that military officials thought was packed with Houthi fighters. More than 40 schoolboys were killed.
Amid a global outcry, the Trump administration warned its Gulf allies that the U.S. might suspend aerial refueling for the coalition if it didn’t take steps to address the problems.
Saudi Arabia admitted its mistakes and vowed to impose new restrictions designed to prevent another tragedy.
That was enough for Mr. Pompeo to certify last month that the Saudi-led coalition was doing what it needed to secure continued U.S. military support.
But, as The Wall Street Journal reported, Mr. Pompeo made the decision over the objections of most of the advisers working on the issue. They urged him to reject that decision “due to a lack of progress on mitigating civilian casualties.”
In their new letter, the senators said they were “skeptical” Mr. Pompeo’s decision was warranted. And they asked him to justify his actions by Oct. 31.
The lawmakers also asked Mr. Pompeo to explain why he certified that the Gulf nations were complying with U.S. laws on weapons sales when the State Department’s certification indicated that there were some instances in which they didn’t meet that condition.
The letter, signed by four Democrats and three Republicans, also including Sens. Jeanne Shaheen (D., N.H.), Jerry Moran, (R., Kan.), Jeff Merkley (D., Ore.), and Chris Coons (D., Del.)., comes a week after a larger group of House lawmakers also questioned Mr. Pompeo’s decision to back the Gulf nations.
More than 50 members of the House asked Mr. Pompeo to justify his support. Mr. Pompeo’s decision was backed by those at the State Department who argued that not doing so would jeopardize billions of dollars in pending weapons sales to the Gulf allies, the Journal reported last month.
Write to Dion Nissenbaum at dion.nissenbaum@wsj.com