CAIRO — The U.N. children's agency on Wednesday suspended cash transfers to 9 million of Yemen's most impoverished citizens under pressure from the country's Houthi rebels.

The move comes at a time when Yemen's local currency has been deteriorating, increasing prices of food and fuel, and sparking fears of a worsening humanitarian crisis.

UNICEF said the decision came after it was unable to set up a call center to get feedback from beneficiaries, without providing further details.

Two individuals familiar with the program said the Houthi rebels who control northern Yemen hindered the launch of the call center because they feared it might reveal their manipulation of the cash transfers. The two spoke on condition of anonymity, fearing reprisals from the rebels.

The Iran-aligned Houthis have been at war with a Saudi-led coalition since March 2015. The rebels have repeatedly been accused of diverting aid to their supporters.

Last week, Houthi security authorities banned the country director of the Adventist Development and Relief Agency from returning to Yemen, according to two individuals familiar with the situation.

The agency has been under pressure from Houthis to use the rebels' beneficiary lists in aid distribution and to use Houthi-linked staffers in ADRA-run health facilities. When ADRA Yemen chief Ephraim Palmero objected, he was notified that he wouldn't be allowed to return to the country, the individuals said.

ADRA is among the most active international relief agencies working in delivering aid to millions of impoverished Yemenis.

ADRA President Jonathan Duffy described working conditions in Yemen as a "very disturbing situation" and said the withdrawal of Palmero's travel credentials is a "threat against delivery" of humanitarian needs.

"ADRA carries out emergency responses and development work on the basis of need alone, giving priority to the most urgent cases of distress making no distinctions on the basis of nationality, race, gender, religious belief, class or political opinions," he said in a statement.

The suspended UNICEF payment is the third since the project was launched in August 2017. UNICEF has said the cash transfers are a "lifeline" to a third of Yemen's people and "contribute to avert the risk of famine and allowed targeted families to buy food and medicine."

The value of the Yemeni rial has been in a steady freefall. The rial traded at 800 to the dollar earlier this week, causing immediate price hikes in goods and prompting the Saudis to inject $200 million to shore up Yemen's Central Bank reserves. Before the civil war erupted in 2015, the rial was around 215 to the dollar.

With 8.4 million people not knowing where their next meal will come from, the U.N. Office for the Coordination of Humanitarian Affairs warned last month that a further slide in the rial could result in an additional 3.5 million Yemenis becoming food insecure, and that more than 2 million are "likely to be at a heightened risk of famine."

While the Saudi-led coalition has imposed a land, sea and air embargo impacting the country's imports — 90 percent of Yemen's needs are imported — the Houthis have put restrictions on delivery and distribution of aid to some 19 million Yemeni living in rebel-controlled lands.

In southern Yemen, where Houthis were pushed out two years ago by the Saudi-led coalition, international relief agencies are also facing security challenges.

Doctors Without Borders said in a statement Tuesday that it suspended its operation in Dhale after staffers came under attack a day earlier. It said no one was injured in the attack.

"Due to the severity of these attacks and the clear lack of safety for the team working there, MSF has been forced to withdraw its staff," the agency said, using its French acronym.