Washington CNN  — 

The U.S. and Turkey have reached a “tentative handshake deal” to increase U.S. and coalition access to Turkish air bases, including the base at Incirlik, according to an administration official.

A finalized deal would give the U.S. crucial access from Turkey into Syria and Iraq that it has long wanted. It could significantly shorten flight times on airstrikes against ISIS compared to flights from current bases in Iraq or aircraft carriers in the Persian Gulf.

“Access to Turkish bases such as Incirlik air base will increase the coalition’s operational efficiency,” said Capt. Jeff Davis, a Pentagon spokesman.

The administration official emphasized strongly that the agreement, which has been a subject of discussion for months, is tentative and still needs to be established as a more formal military agreement. The official noted it’s possible either side could back out before that happens.

It is expected that a final agreement could include provisions for the U.S. to conduct manned airstrikes from Incirlik. Until now, the Turks had not allowed such missions.

At a press briefing Thursday, White House spokesman Josh Earnest would not go into details for “operational security reasons.” On Wednesday, President Barack Obama spoke with Turkey President Recep Erdogan. Earnest said he “can confirm that in the context of that conversation the two leaders did agree that we would deepen our cooperation as we take on this ISIL threat,” another name for ISIS.

Reports of the agreement first appeared in Turkish media.

Senior administration officials said this discussion has been going back and forth for about nine months, but they started to make a lot of progress a month ago and the final deal was struck to launch strikes against ISIS during Obama’s call with Erdogan this week.

There has been in particular a problematic strip of the border where ISIS is congregating and which will be a target of operations out of Incirlik. Right now the U.S. strikes originate thousands of miles away.

The officials pointed out that the last time the Obama spoke with Erdogan was about Kobani, Syria, in October, when Obama decided to do airdrops of ammunition and small arms to resupply Kobani and negotiated with Erdogan for the Peshmerga to cross from Turkey into Syria. One official called that a turning point and said that since then the U.S. has argued that with ISIS becoming an increasing threat, the access was important.

“We’ve come a long way since Kobani,” the official said.