The charges, announced by federal authorities in New York City, came after a sting operation in which investigators recorded and videotaped conversations between the accused and sources posing as drug traffickers.
Authorities said the ring leader of the alleged plot was Joseph Hunter, a former US Army sergeant who served as a sniper instructor during his 21-year stint in the military and who sometimes went by the nickname "Rambo."
Hunter had allegedly acted as a contract killer for years, according to the indictment, and clandestine recordings capture him recounting how he arranged murders or "bonus jobs" for real estate agents.
Authorities allege Hunter recruited a team of four former soldiers from the US, Germany and Poland who had been trained as snipers to protect cocaine shipments by air to New York.
Hunter and two other ex-soldiers also agreed to murder a drug enforcement agent and an informer cooperating with authorities, in return for pay from what they believed was a drug trafficking gang, the indictment said.
The three expected to be paid $700,000 for the murder-for-hire plot, with an additional $100,000 going to Hunter, it said.
Asked by undercover sources if his team would kill only the informer or the law enforcement agent as well, Hunter writes in an email, "They will handle both jobs. They just need good tools," according to the indictment.
"The bone-chilling allegations in today's Indictment read like they were ripped from the pages of a Tom Clancy novel," said US attorney Preet Bharara in a statement.
"The charges tell a tale of an international band of mercenary marksmen who enlisted their elite military training to serve as hired guns for evil ends," he alleged.
"Three of the defendants were ready, willing and eager to take cold hard cash to commit the cold-blooded murders of a DEA agent and an informant."
US investigators tracked the suspects in Asia, Africa and the Caribbean, the indictment said.
Hunter and Timothy Vamvakias, both Americans, and Dennis Gogel, a German national, are charged with five counts of conspiracy related to the alleged assassination plot.
Authorities also charged two others, Slawomir Soborski of Poland and Michael Filter of Germany, with conspiracy to import cocaine and to cocaine on board an aircraft and to distribute it.