“The president has to announce that this is a basically almost a declaration of war on the United States,” the Republican from New York said in a phone interview with The Hill on Wednesday.

King, the chairman of the Homeland Security subcommittee on counterterrorism, said that the US war in Iraq is an unfinished business that poses a threat to the United States.

“We don’t have the luxury of just saying, ‘The war is over. The war’s not going on,’ ” he continued. “There is a war. It’s a threat to the US, and we have to fight back.”

The video of Foley’s execution, dubbed “Message to America,” came almost a month after US President Barack Obama authorized the use of airstrikes on ISIL in northern Iraq.

Rep. King said the video should be “a dramatic wake-up call” for Americans and members of Congress who oppose stepping up military action in Iraq.

“This should show us just how vicious and evil ISIL is,” King continued. “They are a threat to the homeland of the United States, a threat to American interests around the world, and American security around the world.”

On Wednesday, the White House confirmed the authenticity of the video.

The video shows an ISIL militant beheading Foley in retaliation for US airstrikes against the group in Iraq. It also warned that the group would slay kidnapped American journalist Steven Sotloff if the US president did not halt the air campaign.

Foley was on assignment for AFP and the Boston-based media company Global Post when he disappeared in Syria in 2012.

President Obama addressed the world on Wednesday, saying the US would eradicate the “cancer” of ISIL.

“The United States of America will continue to do what we must do to protect our people. We will be vigilant and we will be relentless. When people harm Americans anywhere, we do what’s necessary to see that justice is done and we act against ISIL standing alongside others,” the president said.