The Trump administration says it will designate Yemen's Houthi movement a terrorist organization, in a move that has elicited consternation from international aid organizations and authorities.

Secretary of State Mike Pompeo says the U.S. wants to "deter further malign activity by the Iranian regime" that backs the Houthis.

The designation is set to take effect on Jan. 19 — the day before Trump leaves office and President-elect Joe Biden is sworn in.

"If Ansarallah did not behave like a terrorist organization, we would not designate it" as one," Pompeo said in a statement about the plan. The U.S. accuses the Houthis of carrying out a deadly campaign that has destabilized both Yemen and the Middle East.

The terrorist label would apply to the Houthis, whose formal name is Ansarallah, and to three of the movement's leaders: Abdul Malik al-Houthi, Abd al-Khaliq Badr al-Din al-Houthi, and Abdullah Yahya al Hakim.

The action would establish steep legal hurdles for anyone seeking to conduct business with the Houthis. It would also bar members of the movement from entering the U.S. and render it unlawful for U.S. nationals to provide them with "material support or resources."

That, in turn, poses grave difficulties for international relief groups working to mitigate the deadly chaos in Yemen, which the United Nations has described as the world's worst humanitarian crisis. Wrenched apart by a civil war, a ruined economy and the worst cholera outbreak in modern history, Yemen has been battered by catastrophe for years.

Aid organizations fear that, with Houthis still in control of northwestern Yemen — including the country's capital, Sanaa — the U.S. decision will badly hinder their access to many Yemenis in need of assistance.

"Our humanitarian workers are not armed, not parties to conflict, not taking sides. We must work with, for and among civilians in conflict and crossfire. We must be able to negotiate access for our aid and protection of civilians with all sides to all conflicts. Our humanitarian work must not be criminalized," Jan Egeland, secretary-general of the Norwegian Refugee Council, said in a statement released in advance of the decision.

"Where sanctions threaten to make our normal work illegal," Egeland added, "they threaten the survival of people who depend on it."

The U.S. says it is taking those concerns into account.

"We are planning to put in place measures to reduce their impact on certain humanitarian activity and imports into Yemen," Pompeo said. He added that the U.S. is prepared to work with the United Nations and aid groups to help the humanitarian effort.

The Iran-backed armed group is known colloquially as the Houthi movement because its founder comes from the Houthi tribe, which professes a sect of Shiite Islam. The Houthis captured Yemen's capital, Sanaa, along with much of the country's northwestern territory in late 2014 and early 2015. That region borders Saudi Arabia, which has thrown the weight of its military behind the internationally recognized government that was ousted by the Houthis.

Years of grinding internecine violence have followed. As the internal rivals and their foreign backers traded blows, the Yemeni people found themselves trampled beneath both. Battered from all directions, the country's economy and health infrastructure have eroded to the point that more than 24 million Yemenis — or roughly 80% of the country — are in need of humanitarian aid, according to the U.N.

In labeling the Houthis a foreign terrorist organization, the U.S. would add the group to a list that includes dozens of organizations around the world.

The U.S. move has been anticipated for months. As speculation grew last November, U.N. Secretary-General António Guterres issued a statement warning that Yemen was "now in imminent danger of the worst famine the world has seen for decades."

"I urge all those with influence to act urgently on these issues to stave off catastrophe," he added, "and I also request that everyone avoids taking any action that could make the already dire situation even worse."

The decision to brand the Houthis a terrorist organization fits with the broader U.S. approach to the Persian Gulf region under the Trump administration.

The Trump administration has routinely backed Saudi Arabia, which it considers a close ally, and has sought to counter Iran. The administration withdrew from the Iran nuclear deal in 2018 and has repeatedly sanctioned the country's leaders since then — including a new round of sanctions issued last fall.

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