In a televised address on Wednesday, President Barack Obama vowed to "degrade and ultimately destroy" the Islamic State through a "sustained counterterrorism strategy" backed by a "broad coalition" of allies.
Washington has launched more than 150 airstrikes against Islamic State (IS) militants in northern Iraq since August. The embattled government in Baghdad had requested US military intervention to fend off the rapidly advancing Sunni extremist group.
President Obama said he was prepared to expand the military campaign against the IS into neighboring Syria, the militant group's main base of operations.
"I will not hesitate to take action against ISIL in Syria as well as Iraq," the president said, using an alternative name for the IS. But he ruled out cooperating with Damascus, saying that the Assad regime had lost its legitimacy.
"This counterterrorism campaign will be waged through a steady, relentless effort to take out ISIL wherever they exist using our air power and our support for partner forces on the ground," Obama continued.
The IS has published videos in recent weeks showing the beheadings of two American freelance journalists, James Foley and Steven Sotloff. The brutal murders have increased domestic pressure on the White House to escalate its campaign against the Sunni militant group.
No US ground troops
The president's speech came on the eve of the 13th anniversary of the September 11, 2001 terrorist attacks on New York City and Washington, D.C. Obama said that although intelligence doesn't point to any specific danger to the US mainland from the IS, the militant group could become a direct threat if left unchecked.
The president took pains to emphasize that Washington's latest military intervention would be limited in scope and differ considerably from the previous decade of war.
"I want the American people to understand how this effort will be different from the wars in Iraq and Afghanistan," Obama said. "It will not involve American combat troops fighting on foreign soil."
During the recent NATO summit in Wales, US Secretary of State John Kerry announced a core coalition of allies committed to fighting the IS. The coalition includes Australia, Britain, Canada, Denmark, France, Germany, Italy, Poland and Turkey.
Aftermath of Iraq war
Obama won the 2008 presidential election on the promise that he would end the unpopular war in Iraq. Despite that promise, the president agreed to leave a small residual American force in the country. But negotiations between Washington and Baghdad failed. In 2011, the US withdrew its last combat troops from the country.
More than 4,000 American service members died in the conflict. Estimates of Iraqi casualties range widely depending on the source, but most studies agree that the death toll was well over 100,000.
Last June, the "Islamic State," the successor of al-Qaeda's defeated Iraq affiliate, crossed the Syrian border back into Iraq. The Sunni extremists have rapidly advanced in the northern and western parts of the country, targeting minority Christian and Yazidi religious groups as well as Shiite Muslims.
slk/jm (AP, AFP, dpa)