A car drives near a flag belonging to Islamic State militants at the end of a bridge in southern Kirkuk on 23 August 2014.Reuters/Ako Rasheed

US President Barack Obama has officially agreed to send manned and unmanned surveillance flights to Syria in order to gather intelligence about the Islamic State and its bases before possibly conducting air strikes, officials revealed on Monday.

"This is about gaining situational awareness with respect to possible air strikes in Syria," Los Angeles times quoted an unnamed senior official as saying.

This comes days after the United States hinted that the Obama administration was considering air strikes on Islamic extremists in Syria, which is likely to take a turn with aggressive American assault being planned to uproot the hardliner jihadist group – an event that is likely to be seen as a 'shift' in Washington's position on President Bashar Al-Assad, who would be provided with US aid.

The Pentagon, in its first extensive comments about the Islamic State, conceded last week that the growing prowess of the group, backed by its sophistication, wealth and military might, poses the greatest threat to the United States and might even surpass that once posed by al Qaeda.

"They are an imminent threat to every interest we have, whether it's in Iraq or anywhere else," Defense Secretary Chuck Hagel said last week.

Meanwhile, Pentagon officials were worried that aircrafts conducting the over-flight surveillance could be shot down, either by Syrian army air defences or by the militants, the LA Times further noted citing other officials. But the US has high-altitude U-2 spy planes and a drone that could be used in order to lessen the danger from any anti-aircraft fire.

Obama has repeatedly made clear that Assad has to step down, but has been often criticised for his reluctance to intervene in Syria, lest he drags America into another big confrontation while it already has many conflicts to resolve.

However, the gruesome video of the American journalist James Foley being beheaded last week has rattled the American nerves and brought about a collective mood of consternation and apprehension in the United States. The video along with the Islamic State's stark warning in a letter that the group would "not rest until our thirst for your blood is quenched," seems to have jolted the American government into quick action.

"This is an organisation that has an apocalyptic, end-of-days strategic vision and which will eventually have to be defeated," General Martin Dempsey, chairman of the US Joint Chiefs of Staff, told reporters last Thursday, adding that the mission to eliminate the jihadists cannot be achieved by only concentrating on the Iraqi side, where air strikes are currently being carried out.

"To your question, can they be defeated without addressing that part of their organisation which resides in Syria? The answer is no. That will have to be addressed on both sides of what is essentially at this point a non-existent border," he said.