Story highlights British jets targeted the Omar oilfield in eastern Syria

Defense ministry: Oilfields formed the "mainstay" of ISIS' income

The strikes came hours after UK lawmakers approved the bombing

(CNN) British fighter jets targeted an oilfield held by ISIS in their first airstrikes in Syria, the British defense ministry said.

Late Wednesday, U.K. lawmakers voted 397 to 223 in favor of bombing ISIS in Syria, after rejecting military intervention there in a 2013 vote.

Four RAF Tornadoes were deployed from Akrotiri air base in Cyprus soon after Parliament authorized strikes, returning early Thursday, the ministry said.

In a statement , the ministry said the exploitation of seized oilfields was the "mainstay of Daesh's financial income." Daesh is another term used to refer to ISIS.

"Overnight, RAF Tornado GR4s, supported by a Voyager air refuelling tanker and a Reaper, and operating in conjunction with other coalition aircraft, employed Paveway IV guided bombs to conduct strikes against six targets within the extensive oilfield at Omar, 35 miles inside Syria's eastern border with Iraq," it said.

Read More