The US military plans to widen its surveillance and firepower in conflict zones such as Ukraine and the South China Sea with a major expansion of drone flights, the Wall Street Journal reported.

The Pentagon plans to increase daily flights by 50 percent over the next four years, expanding them from 61 a day now to as many as 90 by 2019, the Wall Street Journal said, citing senior defense officials.

The paper said that up to 10 of the flights could also be run by private contractors, though the non-military flights would not be 'strike missions' such as those used to bomb suspected militants.

A report says that Pentagon officials will increase the number of drone flights per day 50 per cent by 2019. Above, a picture of a MQ-1 Predadtor drone above California

Increased flights be used in other areas such as Iraq, Syria and North Africa, the Journal said.

Reuters and Daily Mail Online could not immediately confirm the report, and representatives for the Pentagon could not be immediately reached for comment.

Unmanned drone flights can be used on reconnaissance missions to gather video, photos and other surveillance data.

They can also be used to launch air strikes, which has been controversial under President Barack Obama.

As many as 10 non-strike flights a day would come from private government contractors using older Predator drones rather than newer long-range models, unnamed officials told the Journal.

News of plans for increased drone activity come shortly after the number of flights per day was decreased from 65 to 60 because of stress on the devices' pilots. Above, a pilot flies a drone in Afghanistan from Nevada

Under the phased-in plan, the US Air Force would reportedly continue to launch 60 drone flights a day, the Army would dispatch 16 and the Special Forces Command could contribute up to four.

The news comes after a report earlier this summer saying that the Air Force was scaling back its use of drones from 65 per day to 60.

Operators flying the devices from a location near Las Vegas are 'burning out' from stress, according to the New York Times.

Pilots have complained of feeling 'perpetually deployed' as they struggle to transition from spending time with their families to bombing targets thousands of miles away.

However, intelligence and military officials value the information from drone flights, and the US has recently spoke with North African countries about using drones on the continent to combat Islamic State's presence in Libya.