WASHINGTON - U.S. Secretary of State Mike Pompeo says he plans to designate Yemen's Iranian-backed Houthi rebels as a foreign terrorist organization, a move the United Nations is warning will likely have "serious humanitarian and political repercussions."

The decision has been expected as one of the State Department's possible actions in the waning days of the Trump administration, amid its increased pressure on Iran. The designation will take effect Jan. 19, a day before the presidential inauguration of President-elect Joe Biden.

In a statement late Sunday, Pompeo said the designation of the Iran-backed Houthis and three of the group's leaders is intended to hold them accountable for acts such as "cross-border attacks threatening civilian populations, infrastructure, and commercial shipping."

The United Nations has warned for weeks that such a designation will hurt humanitarian operations. Yemen relies almost completely on imports for its food supply.

"We are concerned that the designation will negatively impact, including through possible 'over compliance' by commercial actors, imports of food and other essential commodities just as more Yemenis are starving," U.N. Spokesman Stephane Dujarric told reporters Monday. "The humanitarian operation“ the largest in the world - cannot replace the private sector or compensate for major drops in commercial imports of food and other essential goods."

The U.N. says more than 16 million people“ more than half of Yemen's population -- will be facing crisis levels of food insecurity by the middle of this year. A further 3.6 million are on the brink of famine, and that could rise to 5 million by June.

"The growing risk of famine in Yemen underlines the imperative for the U.S. to swiftly grant the necessary licenses and exemptions to ensure that principled humanitarian assistance can continue to reach all people who need it across the country without disruption," Dujarric added.

Pompeo said in his statement that the United Sates is ready to implement measures to reduce the designation's impact on "certain humanitarian activity and imports" into Yemen and is ready to work with the U.N. and NGOs to address the implications.

The U.N. also expressed concern that the U.S. move could hurt its efforts to negotiate a resumption of the political process and further polarize the parties.

"Notwithstanding possible political repercussions, we will continue to work with all parties to resume and continue an inclusive political process to reach a comprehensive negotiated settlement to end the conflict," the U.N.'s Dujarric said.

More than five years of war between the Saudi Arabian-backed government of President Abdu Rabu Mansour Hadi and the Tehran-supported Houthi rebels has pushed the country into chronic state of crisis.

In a separate development, Pompeo spoke at Voice of America's headquarters in Washington on Monday, taking questions on camera for the first time since a mob of supporters of President Donald Trump overran the Capitol last week as lawmakers were certifying Biden's presidential victory.

Last week on Twitter, the secretary wrote that, "In the United States, law enforcement officials quash mob violence so that the people's representatives can exercise power in accordance with the rule of law and constitutional government."

In a highly unusual move, American diplomats drafted two cables condemning Trump's incitement of the deadly assault on the Capitol and calling for administration officials to support invoking the 25th Amendment to remove him from office.

Using what is known as the State Department's "dissent channel," the career foreign service officers said they fear last Wednesday's siege may badly undermine U.S. credibility to promote and defend democratic values abroad.

The cables also reflect anger at the response to the riot by Secretary of State Pompeo.

On Friday, Pompeo met for the first time with Antony Blinken, President-elect Biden's nominee to be his successor at the State Department.