President Obama is weighing in on the Florida church planning to burn the Quran on Saturday.
He calls it "a destructive act", while the FBI warns extremists may fight back.
Pastor Terry Jones has said he'd consider calling off his Quran burning if President Obama asked him to.
That request came in an ABC interview this morning.
"I just want him to understand that this stunt that he's talking about pulling could greatly endanger our young men and women who are in uniform," President Obama said.
The FBI says there's no evidence of a specific threat, but it has "high confidence" from "credible information" that extremists may retaliate.
The State Department has asked every U.S. embassy to assess security.
"It's regrettable that a pastor in Gainesville, Florida with a church of no more than 50 people can make this outrageous and distressful, disgraceful plan," said Secretary of State Hillary Clinton.
The church now has no presence online.
Its Internet provider has pulled both church websites.
"We feel that is an indirect of course violation of our freedom of expression, freedom of speech, because they are trying to shut us down," Jones said in response.
Opposition is mounting from around the world, including New York.
"If you're about religion, whether it is Christian or Muslim, why do you want to offend people?" asked former New York Mayor Rudy Giuliani.
Heightening concerns is the controversy about building a mosque near Ground Zero.
The imam behind that effort now says moving the mosque could cause a violent backlash from Muslim extremists.
