WASHINGTON, Sept. 22 -- The Islamic State (IS) taunted U.S. President Barack Obama in an audio recording allegedly released by the terrorists, just as the U.S. ramps up efforts to destroy the militant group.

The IS has overtaken a vast swath of territory in northern Iraq in a bid to carve out an Islamist state, from which the Obama administration frets the militants could launch a strike against the U.S. homeland, much like al-Qaida used Afghanistan as a staging ground for the Sept. 11, 2001 attacks against New York and Washington.

In response, the U.S. has launched about 170 air bombardments against IS positions, and U.S. Congress last week backed Obama's plan to arm and train moderate Syrian rebels to fight the IS militants.

The U.S. and partner nations have also begun striking the IS targets in Syria, using a mix of fighters, bombers and Tomahawk missiles, the Pentagon said Monday night.

The audio recording warned Americans that "you will not feel secure even in your bedrooms," as reported Monday by NBC News, which could not immediately verify the recording's authenticity.

The statement purportedly featured IS spokesman Abu Mohammed al-Adnani calling Obama "vile" and a "mule of the Jews" and charged him with being "more foolish" than former U.S. President George W. Bush, who launched the U.S. invasions of Iraq and Afghanistan more than a decade ago.

"Are America and all its allies from amongst the crusaders and atheists unable to come down to the ground?" the recording continued, an apparent swipe at Obama's decision not to deploy U.S. ground forces to the war-torn region.

"You will pay the price as you walk on your streets, turning left and right, fearing the Muslims," the recording warned.

An attack on U.S. soil is Washington's ultimate nightmare, as no one wants a repeat of the 9/11 attacks that killed nearly 3,000 victims.

Currently, an estimated 100 U.S. citizens are fighting with the IS, and the White House said this week that some of those radicals have already re-entered the U.S.. It only takes one terrorist to set off a bomb and kill scores of people, experts noted.

But despite a sense of alarm in foreign policy circles and among pundits and media, many have charged Obama with sitting on his hands in face of the terror threat.

After U.S. forces in 2011 killed Al-Qaida terrorist mastermind Osama bin Laden -- a major foreign policy win -- the administration acted as if the terror threat was over, critics charged.

After the IS conquered Fallujah, Iraq, Obama simply dismissed the group as amateurs in a New Yorker interview last January. Now, the IS proves itself to be a deadly foe.

Indeed, Obama's public stance toward the IS has confused observers, and experts said the terrorists are taking note.

"Ever since the president went on prime-time television to announce his new strategy to 'degrade and destroy' ISIS, he and his team have slipped on one banana peel after another," David Gergen, a CNN analyst argued on CNN.com on Sunday.

Gergen also mentioned the administration's muddled messages on whether this is a war or simply a counterterrorism campaign.

"Who knew after so many contradictions from the administration? Is the threat from (IS terrorists) something we are trying to prevent from happening one day or is it imminent? Again, contradictions," contended Gergen, who has been an adviser to four U.S. presidents.

More fundamentally, critics fret that Obama believes simply not antagonizing groups like the IS will keep the U.S. safe. But terrorists perceive this as weakness, and experts say the IS may eventually want to prove its viability by launching a major attack against the world's superpower.

Republican strategist Ford O'Connell told Xinhua that a number of Americans believe that Obama's plan is a half-hearted effort to defeat the terrorists, as the president is reluctant to re-engage Iraq after staking his legacy on being the leader that ended U.S. involvement in the war-torn country.

"It has to do with his base a little bit, but it also has to do with his philosophy with Iraq," he said.