Following the release of a video titled "A Message to the Allies of America," in which an ISIL fighter executes British humanitarian aid worker David Haines, the U.K.'s prime minister, David Cameron, and the White House have released statements condemning what happened and outlining what will be done.

ISIL released the video via Twitter on Saturday and was produced by the al-Furqan Media Foundation, according to SITE Intelligence Group, which has been monitoring ISIL activity online.

Prime Minister David Cameron condemned ISIL’s actions soon after the video surfaced through Twitter.

On Sunday, the British Prime Minister released a longer statement on Facebook deploring ISIL's actions and explaining what British government will do next.

"Today, the whole country will want to express its deep sympathy for David Haines' family," Cameron said in the statement. "They have endured the last 18 months of David's captivity with extraordinary courage."

He then condemned ISIL's actions, calling them "callous and brutal," and pledged Britain's support in finding those culpable.

"We will hunt down those responsible and bring them to justice, no matter how long it takes," he stated. Cameron then proceeded to remember and honor Haines' memory and his humanitarian work, calling him "a British hero."

However, despite threats made against another British hostage if Britain continues its actions against ISIL, Cameron said the U.K. will continue to battle ISIL.

"We have to confront this menace," Cameron said. "Step by step, we must drive back, dismantle and ultimately destroy ISIL and what it stands for," adding that Britain will join its allies in the fight.

"We will not do so on our own - but by working closely with our allies, not just the United States and in Europe, but also in the region," Cameron said, expressing his support to U.S., Iraq and the Kurdish fighters in their struggle against the Islamic terrorist group.

In a show of solidarity, the White House also released a statement condemning the Haines’ execution.

“We will work with the United Kingdom and a broad coalition of nations from the region and around the world to bring the perpetrators of this outrageous act to justice, and to degrade and destroy this threat to the people of our countries, the region and the world,” the statement ends.

David Haines' brother, Mike, also released a statement in remembrance of his brother and the work his did.

"David was most alive and enthusiastic in his humanitarian roles. His joy and anticipation for the work he went to do in Syria is for myself and family the most important element of this whole sad affair," he said.

"He was and is loved by all his family and will be missed terribly."