Democrat Roy Barnes said in a statement that the site in lower Manhattan "is hallowed ground and it is too painful and divisive to build a mosque there."
Nathan Deal said Thursday that as "a potential governor of the state of Georgia" he didn't have a say in what happens in New York.
"I don't think government officials from one place should be telling government officials from someplace else what they ought to be doing," the Republican from Gainesville said.
"But as an American, I am absolutely opposed," Deal said. He called construction of the mosque two blocks from where The World Trade Center once stood "an insult."
"It keeps the wounds of 9/11 alive," Deal said.
Deal's statement Thursday went further than one he offered to the Journal on Wednesday.
"As governor, I don't want New Yorkers telling Georgians what to do with our land. I'll return the favor by staying out of their business," Deal said in an e-mail, according to the newspaper.
The mosque issue has become a political flashpoint this election season, especially after President Barack Obama waded in last week.
Obama has said he believes Muslims have the right to build an Islamic center in New York as a matter of religious freedom, but the following day he said he won't take a position on whether they should actually build it.
That's set off hand-wringing among vulnerable Democrats who fear fallout at the polls on the politically sensitive topic.