There's at least the case of Anwar al-Awlaki, an American citizen who was killed via drone strike authorized by President Obama. Here's a letter then-AG Eric Holder sent to Congress: https://archive.nytimes.com/www.nytimes.com/interactive/2013...
Not only Alwaki himself was killed, but his wife, son, daughter, brother in law, nephew, and few other certainly non-involved relatives over a period of many years.
Strikes, and raids made when US was hunting down his family member killed few dozens more people falsely believed to be his relatives.