Retired Marine Corps Gen. John Allen says the Islamic State group is at an "entirely different level" than al Qaeda and the United States should take its threats very seriously. In an exclusive interview broadcast on ABC's "This Week," Allen said the video released last week showing Jordanian pilot Lt. Muath al-Kaseasbeh being burned to death in a cage could be considered a tipping point in the battle against the terrorist Islamist group.

"ISIS at an entirely different level [than al Qaeda]. It's better organized, has better situational awareness," Allen said, but insisted the coalition has adapted its approach and is making decisive inroads.

"The coalition [against ISIS] is strengthening daily," Allen said, adding ISIS' actions have "redefined barbarity."

Asked if the video released last Tuesday backfired, Allen responded, "Absolutely it did."

"It's a very important moment for our Arab allies in the coalition," he added.

Allen, President Obama's special envoy to the coalition, said the ISIS atrocity has "galvanized the coalition" and unified it. King Abdullah II of Jordan has indicated he wants to do more to eliminate the terrorist group.

Until now, the United States had been responsible for 80 percent of the airstrikes carried out against ISIS targets. Jordan initiated a wave of strikes Thursday, its pilots writing on their bombs ISIS is an enemy of Islam, and has continued for three straight days.

ISIS controls a number of population centers in Iraq, amounting to about a third of the country. It was driven out about a week ago from Kobani, which sits on the Syrian border with Turkey and has been the center of fierce fighting.

Kobani, Allen said, "is a good example" of a decisive blow against the militants. He said as the group, which has some 30,000 fighters, has changed its tactics, so has the coalition.

As to ISIS' charge that Jordan's bombing runs killed the last remaining U.S. hostage in the terrorists' hands -- humanitarian aid worker Kayla Mueller -- Allen said the claim still is being investigated. U.S. and Jordanian officials said there is no evidence ISIS' claim is valid. The group sentenced Mueller to death shortly after her 2013 capture.