U.S. Defense Secretary Ashton Carter said Monday that airstrikes against the Islamic State group -- following Friday's terrorist attacks in Paris -- were necessary, but would not destroy the terrorist group in Syria, Reuters reported. The remarks came as world leaders have grappled with how to respond to the attacks, and were reportedly moving forward with a draft for a ceasefire in Syria.

Carter also told Reuters that the recent threat, purportedly from the Islamic State group, to attack Washington, D.C., was the work of a "lone wolf." The Islamic State group -- also known as ISIS or ISIL -- warned in a video Monday that any countries participating in airstrikes against Syria would face the same fate as Paris, which saw attacks that killed at least 129 people.

Friday's attacks included suicide bombings and shootings at multiple restaurants, a soccer stadium and at a concert hall -- where the largest number of people were killed. More than 350 people have been injured, according to multiple reports.

At least eight assailants were believed to have committed the terrorist attacks, which authorities linked to the Islamic State group. Seven of the attackers were reported to be dead, mostly by detonating suicide vests.

The scene to see the worst carnage was the Bataclan concert hall, where the American rock band Eagles of Death Metal was performing. About 100 people were killed in the hostage crisis at the concert hall, according to CNN.