There's no medicine to treat diarrhea or patients with war injuries.

Patients with cancer and hypertension are also not being treated because of a lack of supplies.

That's the situation in Taiz, Yemen's third largest city, because of a blockade that began in mid-November, a tactic in the civil war that began in September 2014 and greatly accelerated last March, when neighboring Saudi Arabia began a campaign of heavy air strikes in support of the country's recognized government.

While the situation across the country is horrific — the U.N. estimates at least 6,000 have been killed since the air raids began, Yemen's infrastructure is in tatters and 80 percent of its nearly 25 million people require food aid — things are even worse in Taiz. The siege by rebel forces has left its 600,000 residents with no outside lifelines. Now the World Health Organization (WHO) says that because of the blockade it cannot get five trucks loaded with medical and surgical supplies into to the city, which means that Taiz's six hospitals are facing critical shortages of life-saving treatments and equipment.

"We have been trying to get our trucks in really since December 14," says Dr. Ahmed Shadoul, head of the WHO office in Yemen. Among the supplies sitting in idled trucks are medicines to treat diarrhea, trauma kits and 500 canisters of oxygen. The trauma kits and oxygen tanks are essential in for treating patients with war injuries or any patients requiring surgery, he says.

Although all six hospitals remain open, the dwindling amount of supplies — the last time WHO was able to make deliveries was last September — has forced them to curtail some services. "The hospitals are open but not fully functioning," Shadoul says. "The need for these supplies is growing."

Another issue caused by the siege: a shortage of fuel to run generators. So the hospitals are also dealing with a lack of electricity. Such shortages are also affecting hospitals across the country.

While the situation is clearly bad across Yemen, he says, "it is worse there [in Taiz] than elsewhere in the country," because at least WHO has been able to continue to its deliveries of medical supplies to other cities and regions.

The war in Yemen, which sits on the southern end of the Arabian Peninsula, began when its former president and forces loyal to him began backing Houthi rebels. By January 2015, the rebel coalition has gained control of much of the country's western and northern regions, including the capital, Sana'a. The Houthis are Shia tribesmen — the country is around 35 percent Shia and 65 percent Sunni — and are backed by Iran, which is predominately Shia. Saudi Arabia, which is mainly Sunni, entered the fray on behalf of the government forces because it was alarmed at the prospect of having an Iranian puppet state on its southern border.

Taiz is in the southwest, and although it's in an area mainly controlled by the rebels, there are pockets of government resistance forces still operating in the city. Hence the blockade.

Shadoul says that "despite assurance from all relevant parties," the trucks have not been allowed into Taiz. The rebel authorities in Sanaa give permission for the deliveries, he says, but local commanders on the ground refuse to yield. "We are ready to cooperate with any partner who can enter Taiz."

Even before the siege, he says, the war was causing public health problems in the city. A few months ago there was an outbreak of dengue fever, but WHO doctors managed to get it under control.

Meanwhile, the Saudi bombing campaign and other missile attacks have also damaged and destroyed several hospitals and clinics across the country.

Last weekend a missile — it's not clear if it came from a bomber or was surface-based — blasted a hospital run by Doctors Without Borders, or Medecins Sans Frontieres (MSF), in Saada province, a Houthi stronghold. At least four people were killed and 10 injured, three critically.

Bombs destroyed another MSF hospital in Sadaa last October, and a medical clinic in Taiz was bombed in December.

Marta Canas, MSF deputy director of operations and based in Barcelona, says it was not clear if the hospitals were purposely hit. But Shadoul says, so far, "there is no evidence that they've been targeted." It appears, he says, they are collateral damage from strikes against nearby government and military facilities.

How badly the most recently hit hospital was damaged and if it can be put back into operation is unclear, Canas says, because all patients and staff were evacuated, and it's been too dangerous to send staff back to make assessments.

MSF operates 11 hospitals and 18 health clinics across Yemen, and clearly they are already stretched to their limits. Says Canas: "Since last March we have treated 20,000 war-wounded, which is a huge number." But sadly, back in Taiz, as the numbers of people injured or ailing continue to mount, treatments may no longer be an option.

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