Yemen’s Houthi rebels on Tuesday said they were “surprised” by accusations from the United Nations food agency that they are stealing humanitarian aid and accused it of taking sides in the nearly four-year-old war.

The World Food Program on Monday threatened to suspend some aid shipments to Yemen if the rebels did not investigate and stop theft and fraud in food distribution, warning that the suspension would affect some 3 million people.

The Associated Press reported Monday that armed factions on both sides of the conflict are stealing much-needed food aid, diverting it to their fighters or reselling it for profit. Some groups are blocking deliveries to communities they view as their enemies.

Mohammed Ali al-Houthi, head of the rebels’ Supreme Revolutionary Council, said “we were surprised” by the allegations from the World Food Program, which he said “did not communicate officially” with the rebels. He said the decision to go to the media was “a major deviation in the work of the program.”

He called on the WFP to back up its accusations with proof.

Al-Houthi also accused the U.N. agency of sending “rotten food” to the war-torn country, saying authorities refused to allow that food in because “it violates standards and regulations and is not suitable for human consumption.”

“The work of these organizations is mostly politicized ... and this situation reflects that their work has shifted from independent to subordinate to the United States and Britain,” he said.

The U.S. and Britain support a Saudi-led coalition that has been at war with the Iran-aligned rebels on behalf of Yemen’s government since March 2015. The Yemeni government welcomed the WFP’s announcement, saying a “comprehensive correction is needed to the mechanism of humanitarian work in Yemen.”

The World Food Program’s ultimatum was an unprecedentedly strong warning, pointing to how corruption has increased the threat of famine in Yemen, where the war has created the world’s worst humanitarian crisis.

In a letter sent to rebel leader Abdul-Malek al-Houthi, WFP director David Beasley said that a survey done by the agency showed that aid is only reaching 40 percent of eligible beneficiaries in the rebel-held capital, Sanaa. Only a third are receiving aid in the rebels’ northern stronghold of Saada.

“If you don’t act within 10 days, WFP will have no choice but to suspend the assistance ... that goes to nearly 3 million people,” the letter said. “This criminal behavior must stop immediately.”

The WFP said it obtained photographic evidence showing rebels seizing food and manipulating lists of aid recipients.

The U.N. agency helps about 8 million hungry people in Yemen and has been working to increase its scope to reach a total of 12 million. It wants an overhaul of the relief system, including biometric registration, but says the rebels resist such measures.

A separate U.N. team led by a Dutch officer has been monitoring a cease-fire in the Red Sea port city of Hodeida since late December, which ended months of fierce fighting between the two sides for control of the city. Some 70 percent of Yemen’s imports come through Hodeida.

Yemeni officials said the team led by Dutch Maj. Gen. Patrick Cammaert met with the country’s warring parties on Tuesday. The officials spoke on condition of anonymity because they were not authorized to brief the media.

AFP.