Millions of dollars' worth of U.S.-supplied drones that Kiev had hoped would help in its war against Russian-backed separatists have proven ineffective against jamming and hacking, Ukrainian officials say.

The 72 Raven RQ-11B Analog mini-drones were so disappointing following their arrival this summer that Natan Chazin, an advisor to Ukraine's military with deep knowledge of the country's drone program, said if it were up to him, he would return them.

"From the beginning, it was the wrong decision to use these drones in our (conflict)," Chazin, an adviser to the chief of the general staff of Ukraine's armed forces, told Reuters.