As the war in Yemen continues to devastate the civilian population, the Saudi-led coalition’s recent decision to tighten Yemen’s borders to humanitarian aid will only make an unbearable situation immeasurably worse. This drastic act has placed a stranglehold on the few organisations still providing assistance in the country.

My organisation, Médecins Sans Frontières (MSF), is struggling to provide lifesaving medical services in Yemen now that the main borders have closed. Last week, flights that once transported medical specialists into the country have been grounded, and ships that brought lifesaving drugs and medical equipment were diverted from the port city of Aden. While the blockade was partially eased on Friday, the main routes for aid remain closed, and it is unclear how much access will be granted to humanitarian organisations in the coming weeks. To understand the profound effects these measures will have, consider the extent of suffering already.

More than two years of war have unleashed a cascade of deadly consequences across the country, from the unprecedented outbreak of cholera earlier this year, to the severe malnutrition stalking the countryside as the cost of basic food soars. Meanwhile, hundreds of health centres have been damaged or destroyed, deprived of essential supplies or abandoned by health workers who have not received their government salaries for more than a year.

When I visited Yemen in September, I went to the northern city of Abs, where we support the only fully functioning hospital in a rural area. Before the conflict escalated, the hospital was meant to serve about 100,000 people. Today it serves 1 million. There is no other health care available to people who live perilously close to the front lines, about 50 kilometres away.

Patients lined the gravel courtyard of Abs Rural hospital, waiting for treatment in the oppressive heat. All 40 beds in the therapeutic feeding centre were filled with malnourished children. I met Fatma, a nine-year-old who lay listless and emaciated in her billowing purple dress. The staff had treated her for severe malnutrition earlier this year, saving her life with a blood transfusion, but she was back with one of the worst cases of malnutrition they had ever seen. We did not know whether she could survive.

Other patients came with respiratory infections, snakebites, liver failure or broken bones. The week before Yemen’s borders were closed, the hospital had 980 emergency room visits, doctors performed 110 surgeries, and MSF midwives delivered about 20 babies per day. Yet in the latest escalation of the conflict, the Saudi-led coalition is warning humanitarian organisations to avoid "areas of combat," which would further exclude thousands of people from accessing health care in communities transformed into war zones.

Even Abs hospital—protected under international humanitarian law—was bombed by the Saudi-led coalition in August 2016, killing 19 people, including a MSF staff member, and injuring 24. The bombing was and remains unjustifiable.

Many people are unable to access medical care under these circumstances, and millions of people displaced by the war require basic aid.

Before leaving Abs, I visited a windswept camp just east of the city, where displaced people have lived for more than two years. There is virtually no health care or infrastructure in the camp, with clean water trucked in every 10 days. While a person needs about 15 litres of water per day, camp residents told me they only receive about two litres.

Many lacked basic shelter, draping their sun-bleached clothes over foraged sticks and mud to fashion tents. An elderly man named Khatif lifted his shirt to reveal an untreated hernia, bulging from his abdomen. Two of his grandchildren had died since his family fled to the camp. He didn't know why, and he buried them in a field.

The dire needs across Yemen have led MSF to massively scale up medical operations. We have nearly 1,600 staff members across the country, including 82 staff members from abroad, working in 13 hospitals and supporting 18 more. Yet the rising needs far exceed what we can address. While all parties to Yemen’s conflict bear some level of responsibility for the current crisis, the Saudi-led coalition’s continued blockage of the main aid routes into the country is a particularly punitive measure against defenseless civilians.

Already, the impact of the border restrictions is being acutely felt. Fuel prices have skyrocketed, which means those in need of medical care can’t afford to travel to hospitals. Supplies of certain medicines and drugs are beginning to run low. Our medical staff are unable to reach Yemen to provide lifesaving care.

Coalition leaders must immediately grant unhindered access to and within Yemen, so that humanitarian assistance can reach those most in need. The Saudi-led coalition has previously vowed to protect "the entry and exit of humanitarian supplies and crews." For the health and safety of the people of Abs, and millions in Yemen who lack access to clean water, adequate nutrition and basic health care, that promise must be kept.