The unfortunate guest -- a Delta Air Lines pilot in his 30s -- was handcuffed and questioned in the shower of his Boston hotel room for nearly an hour, according to US media reports citing unnamed sources.

The training exercise "was meant to enhance soldiers' skills to operate in realistic and unfamiliar environments," US Army Special Operations Command (USASOC) said.

The team "entered the wrong room and detained an individual unaffiliated with the exercise," USASOC said, expressing "our deepest apologies to the individual who was affected."

The FBI -- whose Boston Division was assisting with the practice raid -- said the incident occurred around 10:00 pm on Tuesday and that Defense Department personnel "were mistakenly sent to the wrong room and detained an individual, not the intended role player."

No one was injured, but police were called and arrived to confirm that "this was indeed a training exercise," the FBI said in a statement.

Police officers responded to a radio call around 12:20 am on Wednesday and went to the luxury Revere Hotel in downtown Boston to investigate, according to a report provided to AFP.

"Upon arrival officers were met by... law enforcement agents," it said.

The USASOC said in its statement, "we are reviewing this serious incident with our partners and no further details will be released at this time."