US President Barack Obama today condemned a preacher's plan to stage a burning of the Koran saying it would be "a recruitment bonanza for al-Qa'ida."
He urged the Rev Terry Jones to "listen to those better angels" and call off his plan.
His plea came as anger grew in the Muslim world with demonstrations in Afghanistan and Pakistan.
Interpol issued an alert warning that the burning could trigger violent attacks.
Obama said in a TV interview what Jones proposes "is completely contrary to our values as Americans. This country has been built on the notion of freedom and religious tolerance."
Florida Governor Charlie Crist said he would closely monitor what happened on Saturday at the Dove Outreach Centre in Gainesville, Florida to try to ensure people are safe.
US embassies around the world will be doing the same after being ordered by the State Department to assess their security. Officials fear the burning could spark anti-American violence, including against soldiers.
"In addition to being offensive, the Gainesville protest puts at risk those brave Americans who are fighting abroad for the freedoms and values that we believe in as Americans," said Crist.
In Afghanistan, officials in Mahmud Raqi, the capital of the Kapisa province some 60 miles north of Kabul, estimated that up to 4,000 people protested at the planned burning. But Nato spokesman James Judge said there were between 500 to 700 people.
Judge added that the Koran burning is "precisely the kind of activity the Taliban uses to fuel their propaganda efforts to reduce support" for coalition forces.
Despite the mounting pressure to call off the bonfire, Jones said he has received much encouragement and supporters have sent him copies of the Koran to burn.
"As of right now, we are not convinced that backing down is the right thing," said Jones, 58, who took no questions at a news conference. He leads a congregation of about 50 Pentecostal followers.
Jones said in an interview with USA Today that he had not been contacted by the White House, State Department or Pentagon. If such a call comes, he said, "that would cause us to definitely think it over. That's what we're doing now. I don't think a call from them is something we would ignore."
At the news conference, Jones was flanked by an armed escort and said he has received more than 100 death threats since announcing in July that he would stage "International Burn-a-Koran Day." The book, according to Jones, is evil because it espouses something other than biblical truth and incites radical, violent behaviour among Muslims.
Muslims consider the Koran the word of God and insist it be treated with the utmost respect. At least one cleric in Afghanistan said it is the duty of Muslims to react and that could mean killing Americans.
Gainesville Mayor Craig Lowe condemned the church's plans and asked residents to watch for suspicious behaviour. At least one counter-protest was planned by a University of Florida student group.
City officials were increasing security, but would not go into detail about how many extra officers will be used, saying only that they were co-ordinating with other cities and tallying expenses.
"We are sending a bill for services to the Dove World Outreach Centre. We're tracking our costs," said city spokesman Bob Woods. "I'm sure the cost will be substantial."
At the church today, six men in suits wearing earpieces spent about a half hour inside the building and then left. They refused to say whether they were federal or local law enforcement agents or otherwise identify themselves.
General David Petraeus, the top US and Nato commander in Afghanistan, told the Associated Press to say "images of the burning of a Koran would undoubtedly be used by extremists in Afghanistan - and around the world - to inflame public opinion and incite violence." It comes as an emotional debate continues over a proposed Islamic centre near the ground zero site of the 2001 terrorist attacks in New York.
Secretary of State Hillary Clinton said that the pastor's plans were outrageous, and along with Defence Secretary Robert Gates, urged Jones to cancel the event.
Ex-Alaska governor and former Republican candidate for vice president Sarah Palin said in a Facebook post that although people have the constitutional right to burn the Koran, doing so would be an "insensitive and an unnecessary provocation - much like building a mosque at ground zero."
The foreign ministries of Pakistan and the Gulf nation of Bahrain issued some of the first official denunciations in the Muslim world, with Bahrain calling it a "shameful act which is incompatible with the principles of tolerance and coexistence." Bahrain is home to the US Fifth Fleet, which is responsible for naval forces in the Persian Gulf.
The president of Indonesia, the world's most populous Muslim nation, has also sent a letter to Obama asking him to stop the bonfire.
In Pakistan, about 200 lawyers and other protesters marched and burned a US flag in the central Pakistani city of Multan.
The Vatican also denounced the protest.
"If Koran is burned, it would be beginning of destruction of America," read one English-language banner held up by the protesters, who chanted "Down with America!"
Jones' Dove Outreach Centre is independent of any denomination. It follows the Pentecostal tradition.Reuse content