While public officials were urging caution in the immediate aftermath of the bomb attack on the Boston Marathon, some were quick to apportion blame.

One of those was conservative commentator Erik Rush, who provoked a furious reaction after seemingly advocating the killing of Muslims in response to the attack. Rush is a columnist for Worldnutdaily and has previously been a guest on Fox News and CNN.

With no information about the attackers yet made public, Mr Rush appeared to imply in a tweet that the culprit was from Saudi Arabia.

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“@erikrush Everybody do the National Security Ankle Grab! Let's bring more Saudis in without screening them! C'mon! #bostonmarathon.”

Then when he was asked by another Twitter user whether he was blaming Muslims for the attack, Mr Rush responded: “Yes, they’re evil. Let’s kill them all.”

Mr Rush later claimed he was being sarcastic went he sent the response.

His comments nevertheless provoked a fierce reaction. One user wrote: “Hope people don't go on the ‘Muslims did it’ bandwagon. Don't be an idiot and know the facts first.”

Another commented: “Apparently someone at Fox News tweeted ‘Kill All Muslims’ after the explosions. As a Boston resident, and as a human being, I'm disgusted.”

Mr Rush responded to one Twitter user who complained about his comments by saying: “Sarcasm, idiot.”

But in subsequent comments on the social networking site he hit out at “Islamist apologists.”

He wrote: “It's nice to see all the Islamist apologists standing up for those who would waste them in a heartbeat.”

Mr Rush, a New York-born conservative columnist and frequent guest on Fox News, gained notoriety during the 2008 election campaign when he highlighted controversial comments made by Barack Obama’s former pastor Jeremiah Wright.

He has also written articles critical of Islam. Last year, Mr Rush wrote a comment piece titled ‘Yes, Islam is an enemy’. In it he argued that Islam was incompatible with American society.

“Islam has never played well with others, and this is because it is a worldview with a creed, dogma and religious aspects, rather than a religion per se. All of these militate against its tolerance of divergent societies and cultures,” he wrote.

He went on: “This is truth: Both the political left and Islamists in America have been exploiting the First Amendment and Americans’ generous nature in order to conquer us.”