The US commander of the Afghan war warned on Tuesday that a decision by American evangelicals to burn the Koran on 9/11 would endanger his troops as the Muslim world reacted angrily to the plan.
General David Petraeus said the planned torching of Islam's holy book by a Florida church would be a propaganda coup for the Taliban in Afghanistan and stoke anti-US sentiment across the Muslim world.
Protests have already gone ahead in the capital Kabul and in Indonesia -- the world's largest Muslim-majority country -- while Iran has warned that the burning could unleash an uncontrolled Muslim response.
The Dove World Outreach Center in Gainesville, Florida, says it will burn copies of the Koran on this weekend's ninth anniversary of the September 11 attacks in protest at what it calls "the evil of Islam".
Afghanistan, where Petraeus leads a 150,000-strong US-led NATO force against an extremist Taliban-led insurgency, is a deeply devout Islamic country where actions seen as against the religion have previously led to deadly violence.
"It could endanger troops and it could endanger the overall effort in Afghanistan," said Petraeus of the plan.
"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," the general said in an emailed statement.
On Monday about 200 men gathered near a mosque in Kabul to protest against the planned torching, shouting "Death to America" and "Long live Islam" for about an hour after their midday prayers, witnesses said.
In January seven tribesmen were killed by gunfire from Afghan security forces trying to disperse angry crowds during a demonstration sparked by allegations that US troops had torched the Muslim holy book.
An investigation by NATO's International Security Assistance Force (ISAF) and Afghan authorities found that no Koran was desecrated following a military operation by the alliance force in the southern province of Helmand.
The planned protest by the 50-member Florida congregation -- who have set up a Facebook page in support of the event bearing the motto "Islam Is Of The Devil" -- triggered a warning from Iran's foreign ministry.
"We advise Western countries to prevent the exploitation of freedom of expression to insult religious sanctities, otherwise the emotions of Muslim nations cannot be controlled," ministry spokesman Ramin Mehmanparast told reporters.
In late August about 100 Indonesian Islamists demonstrated outside the US embassy in Jakarta and threatened "jihad" or holy war if the US Christian group went through with the stunt.
On Tuesday Indonesian Christians said they feared violent reprisals if the burning went ahead.
Indonesian Protestant Christian Churches Union (PGI) has sent a letter to US President Barack Obama asking him to intervene to prevent the book burning, chairman Andreas Yewangoe told AFP.
"The Koran burning will harm world peace. We're deeply concerned as it could create tension here in Indonesia," he said.
The PGI represents about 20,000 churches and nine million followers in Indonesia.
Alleged desecration of the Koran by US troops in both Afghanistan and Iraq has been an incendiary issue in the past, including when a US soldier deployed to Iraq riddled a copy of the holy book with bullets in 2008.
A subsequent demonstration by about 2,000 people in central Afghanistan turned violent, with a Lithuanian soldier and two civilians killed in an exchange of gunfire between protesters and police.
The Florida church's pastor, Terry Jones, said Petraeus' concerns were "legitimate".
But in a statement to the Wall Street Journal, he added: "We must send a clear message to the radical element of Islam. We will no longer be controlled and dominated by their fears and threats."
Interviewed by AFP in July, Jones said: "Islam and Sharia law was responsible for 9/11.
"We will burn Korans because we think it's time for Christians, for churches, for politicians to stand up and say no: Islam and Sharia law is not welcome in the US."