"The United States is at war with ISIL in the same way that we are at war with Al-Qaeda and its Al-Qaeda affiliates all around the globe," said White House spokesman Josh Earnest.
Pentagon spokesman Rear Admiral John Kirby said that the US was not fighting the last Iraq war and used similar language to Earnest.
"But make no mistake, we know we are at war with ISIL in the same way we're at war and continue to be at war with Al-Qaida and its affiliates," he said.
Meanwhile, Secretary of State John Kerry had appeared to be reluctant to term the expansion of US operations against ISIL in Iraq and Syria as "war."
In a series of television interviews Kerry toured the Middle East building an anti-ISIL coalition, he was reluctant to use the term "war" in referring to the US campaign, telling people not to indulge in "war fever."
"We're engaged in a major counterterrorism operation, and it's going to be a long-term counterterrorism operation," Kerry told CBS News.
"I think 'war' is the wrong terminology and analogy but the fact is that we are engaged in a very significant global effort to curb terrorist activity," Kerry said.
Earlier on Wednesday, President Barack Obama authorized airstrikes against ISIL in Syria after launching raids on the Takfiris’ posts in neighboring Iraq.