The United States is preparing military options, including surveillance flights, to pressure the Islamic State (IS, formerly ISIS) in Syria, U.S. officials said on Monday, according to Reuters.
They stressed, however, that no decision had been made to expand U.S. action beyond the limited airstrikes under way in Iraq.
General Martin Dempsey, chairman of the Joint Chiefs of Staff, said last week that IS would eventually need to be addressed on "both sides of what is essentially at this point a non-existent border" between Syria and Iraq.
Dempsey's spokesman confirmed on Monday that options against IS were under review and stressed the need to form "a coalition of capable regional and European partners."
"With Central Command, (Dempsey) is preparing options to address ISIS both in Iraq and Syria with a variety of military tools including airstrikes," Colonel Ed Thomas said, according to Reuters.
"The bottom line is that our forces are well postured to partner with regional allies against ISIS."
A U.S. official said Washington was also preparing to launch intelligence and surveillance flights, including drones, over Syria.
Obama has already launched a campaign of air raids to help regional Kurdish and Iraqi forces fighting IS in the country's north.
IS in response threatened to attack Americans "in any place" if U.S. airstrikes in Iraq hit its people.
Two other U.S. officials also acknowledged the preparation of strike options against Islamic State in Syria, with one saying planning had been under way for weeks.
Still, neither official suggested U.S. military action there was imminent.
The comments echo those of the White House, which said over the weekend it was ready to "take action" against any threat to America as it indicated serious consideration of U.S. military strikes against the IS in Syria.
Republican lawmakers have called on Obama to take more aggressive action to defeat IS in Syria and Iraq, accusing him of policies that have failed to thwart potential new threats on U.S. soil.