The Trump administration has decided to designate Yemen’s Houthi rebels as a foreign terrorist organization, according to four U.S. officials familiar with the matter, a move that aid groups and several senior U.S. officials worry could worsen a humanitarian crisis.

In a statement obtained by The Washington Post, Secretary of State Mike Pompeo announced his intention to blacklist the group and add three of its top officials to a list of “specially designated global terrorists,” including leader Abdulmalik al-Houthi.

A senior State Department official said the decision was based on the group’s involvement in terrorist activities, including a missile attack on a Saudi airport in 2019 and another on a Saudi oil distribution station in 2020.

“The designations are intended to hold Ansarallah accountable for its terrorist acts, including cross-border attacks threatening civilian populations, ­infrastructure, and commercial shipping,” said Pompeo, using the formal name for the Houthi group.

Humanitarian organizations, foreign diplomats and some lawmakers worry that the move could complicate U.N.-brokered peace talks between the Iran-aligned Houthis and the Saudi-backed government in Yemen — parties that have been at war for almost six years in a conflict the U.N. calls the world’s worst humanitarian crisis.

Trump administration officials denied that they were complicating the peace efforts for ­President-elect Joe Biden, who has promised to breathe new life into the diplomatic discussions when he takes office on Jan. 20.

When asked whether the terrorism designation will prevent U.N. or U.S. diplomats from meeting with the Houthis, who are crucial to any lasting political resolution, a senior State Department official said that “we’re going to look at workarounds where we can,” but noted that there isn’t a well-functioning “political track.”

One individual with knowledge of the matter said that the Biden team did not support the designation and that the new administration was expected to vacate it because of the concerns about the humanitarian impact.

In a message Monday on Twitter, Mohammed Ali al-Houthi, a senior Houthi official, said that the movement reserved the right to respond and that “the Trump administration’s policy and behavior is terrorist.”

Nearly a quarter-million people have died in Yemen’s war, a majority of those deaths caused by insufficient food, medical care and other indirect causes.

The Houthis control broad swaths of Yemen, particularly in the north, where aid agencies coordinate with the rebels to deliver badly needed humanitarian assistance.

How the designation will affect Yemenis may hinge in large part on the nature of waivers and exceptions the government grants to aid groups and parties so that they can avoid potential financial and legal penalties, which would include licenses from the Treasury Department’s Office of Foreign Asset Control.

Much of the internal opposition to the decision came from Treasury officials who warned that it would be difficult for them to issue the waivers in an opaque, wartime environment. The officials argued that the department lacks the on-the-ground intelligence to appropriately consider the waivers and therefore opposed making the designation, said diplomats familiar with the situation.

Such protections, even if widely granted, would shield only U.S. government employees and entities from potential prosecution for “material support” to terrorism under laws associated with the “foreign terrorist organization” designation, according to current and former officials with knowledge of the matter.

State officials have said the Justice Department is unlikely to pursue those kind of charges. But such assurances are unlikely to quell the concerns of aid organizations and commercial groups that fear running afoul of U.S. law, fueling additional questions about why the administration is pursuing the designation rather than others without such complications.

The administration’s preparing to announce the designation before Pompeo had signed off on potential waivers and licenses designed to allow aid and commercial activity to continue threatened to intensify the decision’s effect on Yemeni civilians. It also represented the Trump administration’s rush to finalize a growing list of measures targeting Iran before handing off to a new team that is expected to take a different approach to Tehran.

The Trump administration says the Houthis bear the blame for the grim humanitarian situation in the country, citing its use of child soldiers and hampering of the work of aid groups in the country. However, the United States has continued to sell billions of dollars of weapons to Saudi Arabia, which has led a bloody bombing campaign in the country, resulting in numerous civilian deaths.

Trump administration officials, who spoke on the condition of anonymity to discuss a sensitive policy issue, acknowledged that scores of humanitarian aid groups and foreign officials opposed the decision but said that they had exhausted other options and that Houthi rebels refused to meet with them. The United States sent two senior diplomats to the Middle East in December to meet with Houthi representatives, but the group refused the meeting, U.S. officials said.

“We’re looking at ways to draw attention to the fact that the status quo is unsustainable,” said a senior State Department official. “This is going to get people’s attention.”

A United Nations official said there was “grave concern” that the decision could hinder U.N.-led efforts to reach a peace deal, including by raising questions about whether arranging or attending meetings with Houthi officials would be illegal.

The decision could also “polarize even more the positions of the parties to the conflict and hinder efforts to resolve this devastating conflict any time soon,” the official said.

Scott Paul, humanitarian policy lead for Oxfam America, described the move as a “counterproductive and dangerous” decision that would endanger Yemeni lives. In electing to issue an FTO designation, the State Department was embracing “by far the most severe” of the options considered against the Houthi rebels, he said.

“The consequences will be felt acutely across a country also hit hard by extreme hunger, cholera and Covid-19, as banks, businesses and humanitarian donors become unwilling or unable to take on the risk of operating in Yemen,” he said in a statement.

Sen. Todd C. Young (R-Ind.) joined a host of Democratic lawmakers in voicing concern Monday, saying the designation “will further destabilize a war torn country, which is already the home of Al Qaeda in the Arabian Peninsula, cut off our ability to continue negotiations toward peace, and will force the many NGOs in Yemen to stop providing lifesaving assistance in the country.”

The designation represents a turning point in U.S. handling of the war, which began in 2015 when a Saudi-led coalition began what gulf officials hoped would be a short-lived campaign to sideline Houthi separatists who had taken over the Yemeni capital late the previous year.

While Houthi forces have repeatedly launched attacks against Saudi Arabia, U.S. officials have cited only one attack against the United States, when they unsuccessfully fired missiles at an American warship off Yemen’s coast in 2016.

The Trump administration, facing increasing pressure from Congress over U.S. ties with Saudi Arabia and civilian casualties in Yemen, has reduced military support to the gulf coalition, halting aerial refueling of Saudi jets in 2018.

But the Trump administration has increasingly cast Yemen as another front in its campaign against Iran, which has provided military assistance to the Houthis.

Throughout the war, the United States has continued a separate counterterrorism campaign against al-Qaeda in the Arabian Peninsula and the local branch of the Islamic State.

Millions of Yemenis remain in need of nutrition assistance, including hundreds of thousands of children suffering from severe acute malnutrition, according to the United Nations.

Last year, the Trump administration suspended much of its aid to Yemen over Houthi restrictions, making it harder to verify that assistance was reaching intended beneficiaries.

Ali Al-Mujahed in Sanaa, Yemen, contributed to this report.