"My uncle killed by sniper in WW2. We were taught snipers were cowards. Will shoot u in the back. Snipers aren't heroes. And invaders r worse," the 60-year-old filmmaker tweeted before writing a lengthy Facebook post elaborating on what he meant by his comment and insisting he wasn't bashing the hit movie starring Bradley Cooper.
"My dad always said, 'Snipers are cowards. They don't believe in a fair fight. Like someone coming up from behind you and coldcocking you. Just isn't right. It's cowardly to shoot a person in the back. Only a coward will shoot someone who can't shoot back,'" he wrote.
Now some military members are reacting to Moore's remarks.
"The fact that he [Moore] would say something about America's military, snipers in particular, goes to show his abundant lack of intellectual capability that harnesses any value," retired U.S. Marine Corporal Jacob Schick, who appears in the "American Sniper" film, said during a visit to "Fox and Friends."
Former Army Ranger and sniper Nick Irving also weighed in during an appearance on "Fox and Friends," saying, "I don't think [Moore] deserves the breath that I'm about to give, but I'll just say Michael Moore wasn't there in Afghanistan and the last time I checked, he's never shot anybody with a scoped rifle."
When host Elisabeth Hasselbeck asked Irving whether Moore owes him thanks, he said, "I don't really care what he gives me, a 'thank you' or not. A lot of good guys and a lot of my friends died for his right to freedom of speech. I'm not really worried about what he has to say."
Moore, for his part, eventually chimed in specifically about "American Sniper," writing, "Great acting! Powerful message. Sad ending. There."
The film, which received six Oscar nominations last week, topped the box office with more than $100 million over Martin Luther King Jr. weekend.
It follows Cooper portraying real-life Navy SEAL sniper Chris Kyle. Schick is one of three U.S. service members who appear in the movie. Cooper says they helped to add authenticity to the story and sparked pride among the cast members.
"Everybody felt very -- you could just feel it. Everybody felt like it was a privilege every day to be on set telling this story," Cooper said.