President Barack Obama reportedly ignored questions from the press Tuesday afternoon after the jihadist group calling itself the Islamic State (also ISIS or ISIL) released a video that appeared to show a second American journalist being beheaded.

According to a tweet from Time magazine political reporter Zeke Miller, Obama ignored a question that was "shouted" at him as he boarded Marine One and departed the White House for a previously planned trip to Europe. Miller told Business Insider the question was "Sotloff-related."

Bloomberg Television's White House correspondent, Phil Mattingly, subsequently reported Obama got on board Air Force One and left for Estonia without making a public statement following his helicopter flight from the White House.

The president's departure came amid mounting pressure for him to take further action against Islamic State and criticism of his current handling of the group.

Obama is scheduled to spend most of Wednesday in Estonia to discuss tensions with neighboring Russia. The president is also scheduled to be abroad Thursday and Friday. He's expected to attend NATO meetings in the U.K. for both days before returning to Washington, D.C., on Friday.

The official White House photographer, Pete Souza, tweeted this photo Tuesday with the caption: "En route to Estonia, Pres Obama waves from AF1." Twitter/U.S. government On Aug. 20, the Islamic State released a video showing journalist James Foley being beheaded. Following the publication of the second video, purportedly showed Steven Sotloff being executed, a pair of lawmakers issued statements urging the president to take aggressive action to confront the Islamic State.

Obama authorized airstrikes against Islamic State fighters in Iraq late last month; however, he has not launched military airstrikes against the group in Syria. The Islamic State initially formed in Syria during the revolution against that country's President Bashar Assad that began in 2011.

Criticism of Obama's handling of the Islamic State has mounted since a press briefing last Thursday when the president discussed efforts to combat the group and said, "We don't have a strategy yet." Almost immediately after the briefing, the White House press secretary, Josh Earnest, rushed to clarify the president's position and insisted he had a "comprehensive strategy" for dealing with the group.

In his statement on Sotloff's death Tuesday, Sen. Lindsey Graham (R-South Carolina) called for the U.S. to "act decisively" against the Islamic State in both Syria and Iraq.

"Our hearts and prayers go out to the family of Mr. Sotloff and all those who have suffered under ISIL’s barbaric behavior. However, condemnation is not enough to deal with this scourge," Graham said. "It is time we act decisively against ISIL wherever it resides. Whenever American air power has been employed, in coordination with reliable partners on the ground, ISIL has been devastated. It’s a tactic that should be aggressively pursued both in Syria and Iraq."

Graham concluded by referencing Obama's "strategy" remark.

"Mr. President, if you can’t come up with a strategy, at least tell us what the goal is regarding ISIL," said Graham.

Graham was one of two senators who called for action against the Islamic State in the hours after the video of Sotloff's beheading was released.

"Our hearts go out to the family and friends of Steven Sotloff," said Sen. Bill Nelson (D-Florida). "Let there be no doubt, we must go after ISIS right away because the U.S. is the only one that can put together a coalition to stop this group that’s intent on barbaric cruelty."

Sotloff was a Florida native who freelanced for Time magazine and Foreign Policy, among other publications. He was kidnapped by militants upon crossing into Syria a little more than a year ago. He had been freelancing for Time and Foreign Policy.

A little an hour before Obama left the White House, his National Security Council released a statement to Business Insider indicating they were working to verify the "authenticity" of the footage purportedly showing Sotloff's death.

"We have seen a video that purports to be the murder of U.S. citizen Steven Sotloff by the Islamic State of Iraq and the Levant (ISIL). The intelligence community is working as quickly as possible to determine its authenticity," NSC spokeswoman Caitlin Hayden said. "If genuine, we are appalled by the brutal murder of an innocent American journalist and we express our deepest condolences to his family and friends. We will provide more information when it is available."