Targeted drone killings are defended by the United States as means to combat al-Qaeda in the most effective way possible. If attacks are carried out correctly, they should minimize civilian casualties, eliminate risk to our own forces, and remove dangerous militant operatives, ideally dismantling terrorist groups from a safe distance.

But if the attacks are not carried out correctly, as they often aren't, the results can backfire, which is exactly what's been happening in Yemen, according to Reuters

Tribal leaders, who have a lot of influence within Yemen's complex social structure, warn of rising sympathy for al Qaeda. Awad Ahmed Mohsen from Majallah, a southern village hit by a drone strike that killed dozens in 2009, told Reuters that America had brought hatred with its drones. Asked if more people joined al Qaeda in the wake of attacks that killed civilians, Mohsen said: "Definitely. And even those who don't join, now sympathize with al Qaeda because of these strikes, these violations. Any American they see, they exact revenge, even if it's a civilian."

On Thursday, 14 Yemeni civilians were killed by a U.S. drone strike that mistakenly targeted a wedding convoy, according to Yemeni national security officials. Another official, however, said AQAP militants may have been traveling with the wedding party, but in either case it seems that civilians were not the original targets have been killed. The CIA didn't comment on the strike, per standard procedure. The attack threatens to undo the U.S.'s efforts to scale back its drone program, while making it more palatable to the countries it affects.

Reuters reports that al-Qaeda in the Arabian Peninsula (AQAP) has started traveling in smaller groups to avoid the aerial strikes, which may actually make it more difficult to track their motions. And the strikes are angering some Sunni Muslims upset about strikes that kill their supporters, rather than anti-government Shi'ite rebels, fueling sectarian tensions which are already high in the region.

If those killed in this week's attack are confirmed to be civilians, according to the Associated Press, it could mean a surge of anti-American sentiment in Yemen: 

Civilian deaths have bred resentments on a local level, sometimes undermining U.S. efforts to turn the public against the militants. The backlash in Yemen is still not as large as in Pakistan, where there is heavy pressure on the government to force limits on strikes — but public calls for a halt to strikes are starting to emerge.

In May, President Obama promised to increase transparency on the drone strike program and enhance guidelines on their use. But the Bureau of Investigative Journalism found in November that the six months following Obama's speech actually saw an increase of drone strike casualties in Yemen and Pakistan. 

Human Rights Watch and Amnesty International reported in October that civilian casualties of drone strikes are higher than the U.S. admits. Around the same time, a U.N. human rights investigator said 400-600 of the 2,200 people killed by drones in the past decade were noncombatants. And in 2012, reports emerged that the Yemeni government works to help the U.S. hide it deadly errors. 

Data on drone strikes, like all counter-terrorism efforts, is necessarily shrouded in mystery, making it difficult to measure success. But if drone strikes continue to indiscriminately kill civilians, moderates in Yemen may be driven towards more extremist positions. Even governments working with Washington to coordinate the strikes could turn against the U.S. if drone casualties are not scaled back or eliminated.

Drone strikes may very well be an effective means of fighting terrorism, but for now they remain a controversial experiment in warfare that could possibly be drastically, dangerously failing to keep people safe.