(Adds U.S. official's comments on surveillance flights surveillance flights)
WASHINGTON, Aug 25 (Reuters) - The United States is preparing military options, including surveillance flights, to pressure Islamic State in Syria, U.S. officials said on Monday, but they cautioned no decision had been made to expand U.S. action beyond the limited airstrikes under way in Iraq.
President Barack Obama has so far sought a limited military campaign in Iraq focused on protecting American diplomats and civilians under direct threat. Still, officials have not ruled out escalating military action against the Islamic State militant group, which has increased its overt threats against the United States.
General Martin Dempsey, chairman of the Joint Chiefs of Staff, said last week that Islamic State 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 Islamic State 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, using a different name for the Sunni Muslim group that has seized large areas of Iraq and Syria.
"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.
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.
'NOT THERE YET'
Still, neither official suggested U.S. military action there was imminent.
"We're just not there yet," said a senior U.S. defense official, speaking on condition of the anonymity.
Republicans called on Sunday for more aggressive U.S. action to defeat Islamic State militants in Syria and Iraq, accusing President Barack Obama of policies that have failed to thwart potential new threats on U.S. soil.
At the White House, spokesman Josh Earnest said Obama would consult Congress on whatever he decided on Syria, but would not necessarily seek congressional approval. He said Obama had not made any decisions on whether to use airstrikes against Islamic State militants in Syria.
Earnest said the Islamic State threat was a different situation from a year ago when Obama said he wanted Congress to approve the use of airstrikes to stop Syrian President Bashir al-Assad from using chemical weapons on his own people.
Obama sat down for talks on Monday with Defense Secretary Chuck Hagel.
Dempsey, Thomas said, believed that Islamic State needed to be pressured in Iraq and Syria and that defeating the group would require a sustained effort over an extended period of time "and much more than military action."
Although the U.S. air campaign launched this month has caused some setbacks for Islamic State, they do not address the deeper problem of sectarian warfare that the group has fueled with its attacks on Shi'ites.
In retaliation for the airstrikes, Islamic State released a video showing one of its black-clad fighters beheading U.S. journalist James Foley. (Reporting by Phil Stewart; Additional reporting by Missy Ryan; Editing by Bernard Orr and Peter Cooney)