LONDON -- At 4 months old, all Hussain Al-Kholani has ever known is war and want -- he weighs just 4 1/2 pounds, less than a third of the average American baby at that age.
"Hussain's suffered from malnutrition since he was born," Ali Hussein Al-Kholani, the boy's father, told ABC News. "They tell me to take him to the malnutrition clinic in [Yemen's capital of] Sanaa, but I don't have any way to get him there."
Ali Hussein can't work and is forced to feed his family -- his son, daughter, wife and four brothers -- by relying on food handouts from aid agencies. They live in a small hut at the edge of Al-Dahi, a sprawling refugee camp for internally displaced people in the northern province of Hajah. He can't afford to buy his youngest child diapers, let alone travel across the poverty-stricken country to get him treatment.
The story of the Al-Kholani family isn't unique: Some 2 million children require treatment for severe malnutrition, with at least 360,000 at risk of dying, according to the World Food Program. For almost six years of conflict, aid workers have desperately struggled to deliver supplies and medical support to the now 24.3 million Yemenis -- a staggering 80% of the total population -- in need of humanitarian aid.
Added now to the protracted crisis is a new risk of rapid deterioration: One of President Donald Trump's final acts in office -- designating the Houthi militant group Ansar Allah as a "Foreign Terrorist Organization" -- may prevent aid agencies from working in much of the country, and, in the words of one U.S. senator, constitutes a "death sentence for millions."
The situation in Yemen already has been categorized by the World Health Organization as the "world's worst humanitarian crisis." The origins of the conflict are complicated, emerging from the instability of the Arab Spring, but the war has raged since 2015, with both sides suspected of committing war crimes. The Saudis in particular have received international criticism, with the U.S. and U.K. continuing to export arms to the Kingdom, despite accusations that the weapons repeatedly have been used to target hospitals and civilian sites.
Fighting between the Iran-backed Houthi militia and the Saudi-backed government has reached a broad stalemate. The Houthi militia now controls large swaths of the country, while the Saudi-backed government is based in Aden and recognized by the international community.
The most recent incident of violence saw 25 people killed and 110 wounded in a missile attack at an airport in Aden, a city in the south, which Yemen's internationally recognized government blamed on the Houthis -- a reminder that both sides are far from anything resembling a diplomatic settlement. The Houthis denied responsibility for the blast, The Guardian reported.
The country is at a breaking point. In the first six months of 2021, about 16.2 million people, half the total population, are forecast to face "acute levels of food insecurity," according to the WFP, which needs at least $1.9 billion to provide a minimum level of food assistance to avert famine. The UN group is now saying conditions this year are likely to be worse than in 2018, the last time Yemen experienced famine-like conditions.
"How are they going to get food?" David Beasley, the group's executive director, asked the United Nations Security Council last week. "How are they going to get fuel? How are they going to get medicine? It is going to be a catastrophe ... we're going to have a catastrophe on our hands."
Last month, UNICEF warned that Yemen is "teetering on the edge of collapse" and "is perhaps the most dangerous place on Earth to be a child."
"One child dies every 10 minutes from a preventable disease," Executive Director Henrietta Fore said. "Two million are out of school. And thousands have been killed, maimed or recruited since 2015."
For Hussain, and 12 million other children, daily life is a "waking nightmare" – with conflicts seen taking place across 49 different front lines, the group said. As of last year, according to the WFP, 1 million pregnant or breastfeeding women require treatment.
At a malnutrition clinic in Bani Hassan hospital in Hajjah province, Dr. Ali Hajer told ABC News that the food inventory at the center was "zero," as aid supplies had been disrupted over the past few months.
"The war of Yemen destroyed everything, such as economics, health and the living situation in Yemen," he told ABC News. "This assistance is very important. If this humanitarian aid stops for the Yemeni people and the Yemeni children, there will be a huge catastrophe."
COVID-19 is making the situation even more difficult for health workers and humanitarian agencies. As of Jan. 19, there have been 2,119 confirmed cases and 615 deaths, but the WHO is bracing for a second wave at a time when only half of the health facilities in the country are fully or partially functioning. Over the past few years, Yemen has experienced what the WHO called the worst cholera outbreak of modern times, as well as further outbreaks of diphtheria, dengue fever, measles and malaria.
The situation is at risk of deteriorating further. On Jan 12, the United States officially designated Ansar Allah as an FTO, in response to its alleged "terrorist acts, including cross-border attacks threatening civilian populations, infrastructure, and commercial shipping," former Secretary of State Mike Pompeo said in a statement ahead of the designation, adding that the move was "intended to advance efforts to achieve a peaceful, sovereign, and united Yemen that is both free from Iranian interference and at peace with its neighbors."
But the FTO designation now means it's illegal for individuals or groups to provide "material or resources" to Ansar Allah, meaning that without official exemptions, no outside agencies can provide aid to large swathes of the country under their rule.
Aid organizations have said that, in effect, the ruling could make their work impossible to carry out, with supply lines and access already at constant risk of constant disruption. Additionally, they said, the FTO designation won't quell terrorism.
Amanda Cantanzano, senior director for International Programs Policy and Advocacy at the International Rescue Committee, told ABC News that the IRC was "outraged by the decision."
"We see it as something that will create barriers such that it will be nearly impossible for us to effectively and efficiently deliver aid to those in need. And that would be a crisis anywhere. But in Yemen, it is a catastrophe," she told ABC News.
Kirsten Fontenrose, a former NSC senior director for Gulf Affairs, told ABC News that the designation was considered but not pursued in the early years of the Trump administration due to a number of factors. The UN advised that the designation would "make it impossible" to pursue a political settlement in Yemen, but eventually the administration found that Ansar Allah was both "taking advantage of the room to operate to conduct additional terrorist organizations" and "exploiting this vulnerability in the aid community," members of which would oppose the designation.
"Ansar Allah will make sure this designation makes aid work harder," Fontenrose told ABC News. "They want to amplify the voices opposed to the designation, so they need to make the impact look as dire as they can."
Connecticut Sen. Chris Murphy, however, said political sabotage was a more likely motive.
"I think the Trump administration has made a whole series of moves in the last 30 days just tending to try to create chaos for the incoming Biden administration, to try to tie their hands in as many ways as possible," Murphy told ABC News. "You've seen a number of these decisions, including this one in Yemen, the withdrawal of forces from Afghanistan -- there are a number of moves they've made. I think the only reason they're doing it is to just try to make life as miserable as they can."
UN Security Council members have warned there can be "no military solution to the conflict." Martin Griffiths, the UN special envoy for Yemen, said the FTO designation may have a "chilling effect" on bringing the parties together for dialogue.
"What's hard is that the language of the FTO legislation is not meant to apply to a quasi-governmental organization," Jon Alternam, director of the Middle East Program at the Center for Strategic and International Studies, told ABC News. "So it's very sweeping about how you can't have anything to do with these kind of people. ... The Houthis control well over half the population of Yemen. This isn't like dealing with Al Qaeda."
"This isn't to say that the Houthis don't do outrageous things, this isn't to say the Houthis don't endanger civilians all the time -- they do," he said. "But how do you get to a settlement if you criminalize ordinary contact with them?"
Antony Blinken, Biden's nominee for secretary of state, has said that the new administration will "immediately review" the designation. But that may include a fairly complex legal process, and it could take some time to sort out, according to Alternam. Murphy told ABC News that this period could be crucial as Yemenis continue to suffer.
"This is a death sentence for millions of Yemenis because they are, over the course of the next several weeks, going to run out of food and are going to starve to death," Murphy said. "It's that simple. And the fact that the Trump administration went forward with this designation, knowing that that would be the consequence, is absolutely devastating. It's heartbreaking. It's mind-blowing."
For the likes of Hussain and his family, there is no end in sight -- and everyday decisions just get harder and harder.
"[We have] only one food basket from World Food Program," Hussain's father said. "We either sell it to treat the boy. Or take it home so we can eat."
ABC News' Ahmed Baider and Conor Finnegan contributed to this report.