WASHINGTON — (CNN) The U.S. has now conducted the first lethal airstrike into northern Syria from a base in southern Turkey, according to two US defense officials Wednesday.

The strike happened Tuesday and was conducted by a U.S. military drone.

The officials said they were not yet able to announce if the strike was an offensive strike against ISIS, or a potentially defensive strike to protect rebels against Al Nusra fighters.

Armed U.S. fighters jets are not yet flying out of Turkey because both militaries are still working on procedures to de-conflict airspace operations.

The-CNN-Wire ™ & © 2015 Cable News Network, Inc., a Time Warner Company. All rights reserved. (Photo: CNN)