Hillary Clinton has added her name to a long list of those who have condemned plans by a Florida church to burn copies of the Quran on the anniversary of 9/11 as "a warning to radical Islam".

The burning is planned to take place at the Dove World Outreach Centre, a 50-member evangelical Christian church in Gainesville, Florida. Its pastor, Rev Terry Jones, told CNN that he is taking the widespread criticism "seriously", but refused to say whether the event would be cancelled.

He reiterated once more that the burning was intended to send a message to radical Islam that "if you attack us, we will attack you". More than 9,000 people have now joined the Facebook group "International Burn a Koran Day".

The US secretary of state expressed her disapproval at a dinner last night to celebrate the breaking of the Ramadan fast, calling the proposed burning a "disrespectful, disgraceful act". She went on to say:

I am heartened by the clear, unequivocal condemnation of this disrespectful, disgraceful act that has come from American religious leaders of all faiths, from evangelical Christians to Jewish rabbis, as well as secular US leaders and opinion-makers.

Chief among these fellow critics is the US and Nato commander in Afghanistan, General David Petraeus, who yesterday warned that the burning could endanger US troops abroad. He said:

It is precisely the kind of action the Taliban uses, and could cause significant problems. Even the rumour that it might take place has sparked demonstrations such as the one that took place in Kabul yesterday. Were the actual burning to take place, the safety of our soldiers and civilians would be put in jeopardy and accomplishment of the mission would be made more difficult.

As well as Clinton and Petraeus, the White House press secretary Robert Gibbs, the attorney general, Eric Holder, the archbishop emeritus of Washington, Cardinal Theodore E McCarrick, and dozens of other faith leaders have all condemned the burning.

The same Florida church hit the headlines last year for selling T-shirts emblazoned with the slogan "Islam Is of the Devil".

This latest incident marks a growing trend of anti-Muslim sentiment in the US, most notably demonstrated by the furore over the building of a mosque and community centre two blogs away from the Ground Zero site.

With the US midterm elections fast approaching, a certain faction of the Republican right seems to have succeeded in incorporating this kind of extremist reaction to Islam into legitimate political debate, with figures such as Clinton and Petraeus forced to address what might previously have gone unnoticed as a ridiculous and disgusting act by a tiny minority.

Now that the Democrats are in danger of losing both the Senate and the House, they must find a way to counter the effects of this strategy before it makes a lasting and regrettable impact on November's vote.