The U.S. has said on Wednesday that it is withdrawing a dozen warplanes from a Turkish air base, barely a month after they arrived to help Turkey protect its air space and to conduct airstrikes against Daesh targets in Syria and Iraq.

The decision was announced by U.S. European Command, one day after Defense Secretary Ash Carter visited Incirlik Air Base, where the six F-15 Eagles and six F-15 Strike Eagles arrived last month. A Pentagon spokesman, Navy Capt. Jeff Davis, said the timing was a coincidence.

The U.S. still has 12 A-10 close-air support aircraft based at Incirlik, as well as drone aircraft.

During his visit to Incirlik, Carter said he is looking for ways to do more to hasten the defeat of the Daesh terrorists.

Carter asked for more assistance from Turkey on Tuesday to help destroy Daesh terrorists as he kicked off a tour of the Middle East that aims to drum up regional support for the military campaign.

"Turkey has an enormous role to play," said Carter, on his first trip to Incirlik as defense secretary. "We appreciate what they're (Turkey is) doing. We want them to do more."

That includes Turkish forces joining "in the air and the ground as appropriate," Carter told reporters traveling with him. "The single most important contribution that their geography makes necessary is the control of their own border."

Incirlik has grown more important in the U.S.-led campaign of air strikes against Daesh, with 59 U.S., Turkish, Qatari and German aircraft now operating out of the base, up from about 15 from all coalition countries at the beginning of September, U.S. officials said.