WASHINGTON (CNN) -

After three years of avoiding it, President Barack Obama finds himself being pushed toward military action in Syria.

Defense Secretary Chuck Hagel and Joint Chiefs Chairman Gen. Martin Dempsey both made clear that defeating Islamic State jihadists' rampage through northern Iraq would require going after them in neighboring Syria.

"That will have to be addressed on both sides of what is essentially at this point a non-existent border," Dempsey told reporters Thursday.

On Friday, Deputy National Security Adviser Ben Rhodes said the administration was looking beyond the current airstrikes within Iraq's borders.

"If we see plotting against Americans, see a threat to the United States emanating from anywhere, we stand ready to take action against that threat," Rhodes told reporters.

The United States is already gathering intelligence on the locations of ISIS leadership and troops in Syria, two U.S. officials said.

Separately, U.S. officials said the military has been talking about increasing airstrikes in Iraq and possibly carrying out tailored airstrikes inside Syria against ISIS targets.

ISIS savagery

The ISIS fighters are helping Obama make his case with their savagery, which includes mass killings, abductions and other atrocities, such as the video-taped beheading of captured American journalist James Foley.

But the President, who has declined to arm rebels fighting the government of Syrian President Bashar al-Assad, faces a policy change certain to embolden critics in both parties of his reticence back then.

Obama had avoided what he called reckless interventions of the past, particularly the Iraq War, launched by his predecessor.

Critics could argue that Obama's decision to previously keep out of the Syrian conflict contributed to ISIS' growth.

His former secretary of state, Hillary Clinton, has distanced herself from him on Syria strategy during his first term as she prepares for a possible presidential run in 2016.

Legal barrier evaporated

The Obama administration has acknowledged sending U.S. forces into Syria earlier this year in a failed attempt to free Foley.

That established a precedent of acting in Syria to protect U.S. citizens and interests, superseding any legal considerations such as being asked by the host government to enter, argued Frederic Hof, Obama's former point man on Syria.

"There's a pretty good possibility that we and/or some kind of multinational effort will engage in hitting ISIS targets inside Syria," he said.

Iraq escalation

Obama already escalated U.S. military involvement in Iraq to combat ISIS less than three years after ending a lengthy war there.

In June, he sent military advisers to work with Iraqi and Kurdish forces against the lightning ISIS sweep through the north. Earlier this month, the President authorized limited airstrikes on ISIS targets and sent additional advisers to Iraq to protect U.S. personnel and minority groups threatened by the Sunni extremists.

Hagel emphasized the ISIS threat on Thursday.

"They marry ideology, a sophistication of strategic and tactical military prowess. They are tremendously well-funded," he told reporters. "This is beyond anything that we've seen."

Broad-based approach

Hagel and Dempsey also said that defeating ISIS requires a broad-based approach that includes forging an international coalition and better governance in Iraq and Syria to build public opposition to the extremists.

"Political reform will make it harder for (ISIS) to exploit sectarian divisions," Hagel said. The United States and other powers will shore up Iraq at the same time.