Two mischievous straphangers broke into the conductor’s booth aboard a Brooklyn-bound R train in Manhattan on Thursday night and announced over the loudspeaker that they were ISIS members set to “blow up the train,” police sources said.

The duo pulled the apparent prank around 11 p.m. as the R train was between the 23rd Street and Union Square stations, and then fled laughing at the next stop, sources said.

Passenger Lauren Crozier, a 30-year-old actor, was aboard the train heading to her home in Sunset Park when the declaration came over the loudspeaker.

“At first there was some singing, it wasn’t really audible,” Crozier told The Post. “Then we heard, ‘All hail ISIS! Jihad, Jihad, Jihad!’”

“Everyone took their earbuds out and stared at each other,” she said. “I’m not sure any of us thought it was a credible threat. Not after the first moment, anyway. Everyone kind of gave an ‘Oh, hell no’ look to each other.”

Crozier said the suspects making the announcement also said, “This train has been hijacked.”

She said that once the train pulled into the next station, “the whole train emptied out.”

Crozier added that she wasn’t that scared at hearing the announcement.

“No one seemed petrified. We all shared that kind of New York experience, we shrugged it off.”

The train was taken out of service and taken to the Jamaica Yards in Queens, where an investigation was conducted, sources said.

A police source said “it was a hoax and there was no credible threat.”

It’s unclear how the suspects broke into the conductor’s booth.

Police say the suspects are in their 20s.