ABC's Jonathan Karl reported President Obama's plan for a Syrian strike could be "significantly larger" than most anticipated Thursday on "World News Tonight."

Karl quoted an unnamed national security official who claimed the attack could do more damage to Assad in 48 hours than the Syrian rebels have done in two years:

JONATHAN KARL: […] ABC News has learned the president's national security team is preparing for a significantly larger military attack than most had anticipated. The air campaign which is expected to last at least two days will potentially include an aerial bombardment of missiles and long range bombs fired from B-2 and B-52 bombers flying from the United States. That in addition to a relentless assault of Tomahawk missiles fired from those four Navy destroyers in the eastern Mediterranean. Those ships are loaded with nearly 200 missiles, plans call for firing the vast majority of them. As one senior national security official told ABC News, this military strike could do more damage to Assad's forces in 48 hours than the Syrian rebels have done in nearly two years of civil war. That's more than President Obama seemed to be suggesting just days ago.

PRESIDENT OBAMA: What we are envisioning is something limited […] We send a shot across the bow saying stop doing this.