The United States is to conduct surveillance flights over Syria but no decision has been taken to attack Islamic militants there.

President Barack Obama authorised the flights to gather intelligence on Islamic State militants.

The White House said that Mr Obama had not made a decision to take additional military action at this time.

Director of the Centre for Middle East Studies at the University of Oklahoma Joshua Landis said the US felt entitled to get involved partly because of the recent killing of the journalist James Foley.

He said, however, that President Obama must be clear about what he intends to do in the long term.

The Wall Street Journal first reported the planned flights, which it said are due to begin "shortly".

For more than two weeks, US warplanes have carried out a limited air campaign against IS militants in Iraq, with most of the bombing raids conducted near Mosul dam in the country's north.

The murder of Mr Foley by IS jihadists and mounting concern in the West over the threat posed by the extremists has prompted speculation Washington may expand its air war to Syria.

US Central Command, which oversees US forces in the Middle East, has asked for additional surveillance planes to collect more intelligence on potential IS targets in Syria, the Journal reported.

The surveillance planes would provide information in addition to that already collected by US satellites and informants, the report said.

US officials have said privately that the US has no plans to seek consent from the Damascus regime for any military flights and analysts say Syria's air defence systems may not be in working order in the country's east.

The US sent aircraft into Syria in July in an unsuccessful bid to rescue a group of Americans held by IS militants.

The hostages had already been moved when US forces arrived.

At least 191,000 people have been killed in Syria since the start of the more than three-year-old insurgency to oust President Bashar al-Assad.

Islamic State, an offshoot of al-Qaeda which draws some of its strength from foreign fighters, has emerged as the strongest group in the insurgency.

Its thousands of fighters control roughly a third of Syria, with territory in the north and east.