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President Obama sent seemingly conflicting signals Wednesday about his ultimate goal in the fight against the Islamic State, saying at a press conference in Europe that the aim is to "degrade and destroy" the terror group -- but moments later, claiming he wants to make it a "manageable problem."

The president spoke as lawmakers on Capitol Hill and others urge the White House and Pentagon to pursue a tough approach against the Islamic State, also known as ISIS or ISIL.

Those calls mounted after the group released another video showing the execution of an American journalist; the White House on Wednesday confirmed that video as authentic.

Speaking in Estonia during a visit to Europe, Obama at first took a hard line. He condemned the execution as "horrific" and "barbaric" and vowed "justice will be served."

After taking some heat for admitting last week that "we don't have a strategy yet" to address the militant group in Syria, Obama said they do have a regional strategy. Ultimately, he said, "our objective is clear, and that is to degrade and destroy ISIL so it is no longer a threat not just to Iraq but also the region and to the United States."

But later in the press conference, Obama returned to the topic and noticeably softened his tone.

He clarified that if the U.S. is joined by an international coalition, they can "continue to shrink ISIL's sphere of influence, its effectiveness, its financing, its military capabilities to the point where it is a manageable problem."

The remarks are likely to sow confusion on Capitol Hill, and possibly among allies.

"Are we going to contain ISIS or are we going to crush ISIS? And the president has not answered that," Rep. Adam Kinzinger, R-Ill., told Fox News, reacting to the president's remarks.

Sen. Saxby Chambliss, R-Ga., in a written statement, criticized the president's "mixed messages" on the Islamic State. "The time to stop and destroy ISIL is now," he said.

Speaking Tuesday night on Fox News, Sen. John McCain, R-Ariz., said the Islamic State has "got to be destroyed" and claimed the president does not yet have a strategy to implement that.

The president is in Europe this week for meetings with allies, where everything from ISIS to the crisis in Ukraine will be on the table. Meanwhile, Secretary of State John Kerry is heading to the Middle East to try and build a stronger coalition to go after the Islamic State while boosting the Iraqi and Kurdish governments.

The Obama administration, in the face of calls for swift action, has stressed that the problems in Iraq must be addressed in large part by a new and inclusive government in Baghdad. But he continues to weigh whether to expand the current airstrike campaign in northern Iraq into Syria.

On Wednesday, Obama still did not give a timeline for deciding on a strategy to go after the extremist group's operations in Syria. "It'll take time to roll them back," the president said.

As for the execution of freelance reporter Steven Sotloff, two weeks after journalist James Foley was similarly killed, Obama vowed the U.S. would not forget the "terrible crime against these two fine young men."

"Our reach is long and justice will be served," Obama said.

Sotloff reportedly held dual American-Israeli citizenship. In the Sotloff video, a masked militant warns Obama that as long as U.S. airstrikes against the militant group continue, "our knife will continue to strike the necks of your people."

Obama responded that he will continue to fight the militant threat and the "barbaric and ultimately empty vision" it represents.

"Our objective is to make sure that ISIL is not an ongoing threat to the region," he said. "And we can accomplish that. It's going to take some time and it's going to take some effort."

Sotloff, a 31-year-old Miami-area native who freelanced for Time and Foreign Policy magazines, vanished a year ago in Syria and was not seen again until he appeared in the video that showed Foley's beheading. Dressed in an orange jumpsuit against an arid Syrian landscape, Sotloff was threatened in that video with death unless the U.S. stopped airstrikes on the Islamic State.

In the video distributed Tuesday and titled "A Second Message to America," Sotloff appears in a similar jumpsuit before he is apparently beheaded by a fighter with the Islamic State, the extremist group that has conquered wide swaths of territory across Syria and Iraq and declared itself a caliphate.

British Foreign Secretary Philip Hammond told the BBC Wednesday that the masked, British-accented jihadist appears to be the same person shown in the Foley footage.

The Associated Press contributed to this report.