Burnt vehicles are pictured in front of the damaged the Doctors Without Borders-backed al-Quds hospital after it was hit by airstrikes, in a rebel-held area of Syria's Aleppo, April 28, 2016. (Abdalrhman Ismail/Reuters)

The al-Quds hospital in Aleppo targeted in Wednesday night's attacks was one of 150 hospitals supported by Doctors Without Borders in Syria. The organization directly runs six in the country, but provides funding and medical supplies to other medical facilities.

The international charity group, also referred to as Médecins Sans Frontières (MSF) in French, said the medical facility was directly hit and reduced to "rubble."  The organization has condemned the overnight attack, which also claimed the life of one of the area's last pediatricians.

"Where is the outrage among those with the power and obligation to stop this carnage?” said Muskilda Zancada, the MSF head in Syria, in an online statement.

The United Nations estimates that at least half of Syria's hospitals have been destroyed, and the spark of attacks on hospitals is an especially disturbing trend. In armed conflict, hospitals are protected by international law. Yet the facilities supported and run by the Nobel Prize-winning organization have frequently come under attack. And it's not only medical structures. The group said five rescue workers from the Syrian Civil Defense organization have also been killed.

Here is a look at the three recent attacks on Doctors Without Borders hospitals:

1. Kunduz, Afghanistan. "By evening, a hospital. By morning, a war zone"

Doctors Without Borders medical personnel treat civilians injured following an offensive against Taliban militants by Afghan and coalition forces at a hospital in Kunduz. (Doctors Without Borders/AFP via Getty Images)

On Oct. 3, 2015, U.S. military forces "mistakenly struck" a hospital as they attempted to help Afghan forces. The attack killed 44 people and injured 30. The hospital was deemed a neutral zone, even for Taliban militants fighting Afghan forces who were being treated there.

Inside the hospital, which the international relief agency in recent years had turned into the province’s most advanced medical facility, doctors and nurses were busier than ever. Between Sept. 28 and Oct. 3, exhausted hospital staffers treated 394 people, many of whom had received gunshot wounds during the battle for the city.

All that week, a steady stream of Taliban fighters appeared at the hospital seeking treatment, adding to the patient load, according to a hospital security guard.

Before fighters were admitted onto hospital grounds, the guard said, they were required to hand over their assault weapons to facility guards. Once inside, the Taliban fighters — many of whom had been shot — were treated like any other patient.

2. Saada, Yemen. "Medical facilities becoming routine casualties in conflict zones"

On Oct. 27, 2015, a Saudi-led airstrike campaign destroyed a hospital in northern Yemen, injuring one staff member. All others escaped. As my colleague Thomas Gibbons-Neff notes, hospitals must be given prior warning to evacuate before they can be targeted as a military facility.

The loss of another hospital to destruction from the air is just one more instance in a disturbing month-long trend that has spanned multiple conflict zones.

Hospitals are protected areas under the International Law of Armed Conflict and are only viable military targets if the hospital is being used for a military objective. Even then, however, the facility must be given ample time to evacuate before it can be legally targeted.

3. Syria

On Feb. 15, 2016, two airstrikes hit northern Syrian hospitals supported by Doctors Without Borders. The attacks killed at least 25 people and injured 11, according to reports. Data compiled by the organization shows that a total of 94 attacks have hit facilities supported by the group.

This image taken from video provided by the Syrian activist-based media group Maara Media Center shows Syrian Civil Defense rescuers running from the site of a second explosion near a hospital run by Doctors Without Borders in Maaret al-Numan, Idlib, Syri. (Maara Media Center/AP)

Read more:

International Red Cross official sees ‘disturbing trend’ in attacks on hospitals in conflict zones

War in Yemen is pushing health-care facilities to the brink of collapse

What the ruins of Kobane tell us about the destruction of Syria