Differences have emerged between Washington and Ankara over how to use a Turkish air base near the Syrian border in the fight against Islamic State militants.
Ankara’s decision in recent days to open the Incirlik airbase to U.S. jets was reportedly described as a “game changer” by one U.S. official in the battle against the Islamic State group.
Taking off from Incirlik, which is located 110 kilometers (70 miles) from the Syrian border, allows U.S. jets could reach their targets much faster than from the locations they've been using – mainly bases in Bahrain and Jordan, and aircraft carriers in the Persian Gulf.
For months, Ankara resisted Washington’s calls to allow flights from Incirlik because the U.S. was focused on fighting Islamic State militants inside Syria instead of Syrian President Bashar al-Assad's government.
A surge in Islamic State activity in Turkey caused President Recep Tayyip Erdogan to relent, but he said the use of the base by the U.S. would be "within a certain framework."
However, State Department spokesman John Kirby said Incirlik could be used as part of its continuing air support to Syrian Kurdish militia belonging to the PYD in its fight against the Islamic State group.
But Kirby’s Turkish counterpart, Tanju Bilgic, said supporting the Kurdish militia was not part of the agreement.
Ankara views the PYD as an affiliate of the Kurdish rebel PKK, which has been fighting the Turkish state for three decades for greater minority rights.
The PYD, with U.S. air support, has scored a series of victories against Islamic State militants, who have taken control of nearly half of the Syrian territory that borders Turkey.
Sinan Ulgen, visiting scholar at the Carnegie Institute in Brussels, said the opening of Incirlik is about controlling the PYD, rather than helping it.
"Turkey increasingly realized that if it was not willing to do more in terms of fighting ISIS, might be detrimental to Turkey’s national interest in geopolitical terms,” Ulgen said, using another name for the Islamist group.
“Because another objective of Turkey is to prevent the Kurdish PYD from acquiring more territory," he said.
The use of Incirlik by U.S. forces, especially in conflicts with Turkey's neighbors, is always a sensitive subject for Ankara, and Turkish governments are very careful about wording terms of its use.
But analysts say unless there is a clear agreement on the use of Incirlik, the potential for disputes will remain, warning that Ankara in the past is very skillful in manipulating its use to secure its objectives.
Still, the opening of the base will help improve bilateral relations, said Kadri Gursel, a diplomatic expert and writer for the Al Monitor website.
"It’s important because it's a major step for Turkey to be considered as a full-fledged member of anti-ISIS coalition,” Gursel said. “The only criteria was Incirlik, if Turkey opening Incirlik to real airstrikes."