The United States has waged a drone war in Yemen for 16 years, trying to suppress al-Qaida's branch here. But the campaign has had a hidden cost: civilians cut down by the drones' missiles.

There is no comprehensive count of civilian deaths because of the difficulty of confirming identities and allegiances of those killed. But in an examination of drone strikes this year alone, The Associated Press found that at least 30 of the dead likely did not belong to al-Qaida.

That is around a third of all those killed in drone strikes so far in 2018. The Pentagon does not release its assessment of the death toll, but an independent database considered one of the most credible in tracking violence in Yemen counted 88 people — militants and non-militants — killed by drones this year.

The AP count gives a glimpse, even if incomplete, into how often civilians are mistakenly hit by drone strikes, at a time when the Trump administration has dramatically ramped up the use of armed drones. It has carried out 176 strikes during its nearly two years in office, compared to the 154 strikes during the entire eight years of the Obama administration, according to a count by the AP and the Bureau of Investigative Journalism.

The AP based its count on interviews with witnesses, families, tribal leaders and activists. Most of those killed, 24, were civilians; at least 6 others were fighters in pro-government forces — meaning ostensibly on the same side as the U.S. — who were hit in strikes away from the front lines while engaged in civilian life. The drone toll goes almost unnoticed in the region's conflicts. Immensely greater destruction has been wreaked by U.S. allies in the Saudi-led coalition's air campaign against Iranian-backed Shiite rebels known as Houthis. Saudi Crown Prince Mohammed bin Salman, the former defense minister, and Saudi Arabia's allies launched Operation Decisive Storm in March 2015. The Saudi and UAE-led war in Yemen has caused growing international unease after high-profile coalition air strikes killed scores of civilians, many of them children. More than 57,000 civilians and combatants have been killed in Yemen's civil war, by some estimates, and thousands more may have died of starvation caused by the conflict.

In comparison, the toll from U.S drones in Yemen runs in the hundreds, including both militants and civilians. Several databases are trying to track the deaths, with varying results. The Bureau for Investigative Journalism counted up to 1,020 killed by strikes from 2009 to 2016, under President Barack Obama, compared to up to 205 killed in 2017 and 2018. Another database, by the Armed Conflict Location & Event Data Project, counted 331 killed the past two years. Counting civilians among those numbers is complicated by the difficulty in determining who belongs to al-Qaida in a country of multiple warring militias. Al-Qaida has joined the battle against the Houthis, and many of its fighters are incorporated into militias armed and funded by the U.S.-backed coalition.