The top US commander in Afghanistan has warned that troops' lives will be in danger if an American church sticks to its plan to burn copies of the Koran.
Gen David Petraeus said the action could cause problems "not just in Kabul, but everywhere in the world".
Pastor Terry Jones, of the Dove World Outreach Center, plans to put copies of the holy book in a bonfire to mark this week's anniversary of the 9/11 attacks.
The White House and Nato have also expressed concern over the plan.
White House spokesman Robert Gibbs said on Tuesday that "any type of activity like that that puts our troops in harm's way would be a concern to this administration".
Earlier, the US embassy in Kabul issued a statement condemning the plans by the non-denominational church in Gainesville, Florida.
"It could endanger troops and it could endanger the overall effort," Gen Petraeus said in a statement to US media. "It is precisely the kind of action the Taliban uses and could cause significant problems.
"Not just here, but everywhere in the world, we are engaged with the Islamic community," added Gen Petraeus, who heads a 150,000-strong Nato force against a Taliban-led insurgency.
Meanwhile, Nato chief Anders Fogh Rasmussen on Tuesday blasted the church's plans, telling reporters that burning Korans violated the Nato alliance's "values".
"There is a risk that it may also have a negative impact on security for our troops," news agency AFP quoted him as saying.
Mr Jones said the church was "very concerned" after hearing Gen Petraeus' warning and was taking his words seriously. He said the church was praying on the matter but he said the group had "firmly made up our minds".
"How long do we back down?" he said on CNN.
News of the bonfire has sparked protests in Afghanistan and Indonesia.
In Kabul on Monday, about 500 protesters chanted "long live Islam" and "death to America" as they set fire to an effigy of Mr Jones.
The controversy comes at a time of already heated debate in the US over a proposal to build a mosque and Islamic cultural centre two streets from Ground Zero, site of the 9/11 attacks, in New York.
The planned protest by Mr Jones's previously little-known 50-member Florida church, whose website labels Islam "violent and oppressive", has prompted protests elsewhere, too.
Thousands of mostly Muslim demonstrators rallied around Indonesia last weekend.
Claims that US soldiers have desecrated the Koran in both Afghanistan and Iraq have caused bloodshed in the past.
There were deadly protests in Afghanistan in 2008, when it emerged that a US soldier deployed to Iraq riddled a copy of the holy book with bullets.
And further lives were lost in Afghan riots in 2005 when Newsweek magazine printed a story alleging that US interrogators at Guantanamo Bay had flushed a copy of the Koran down a toilet.
The story later turned out to be false and was retracted by the magazine.