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.

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