A handout photo realesed on Sept. 21, 2014, by the Turkish presidential press office shows President Recep Tayyib Erdogan (2nd L) and his wife Emine (L) greeting some of the freed Turkish consulate hostages at the Cankaya presidential palace in Ankara. AFP PHOTO/ PRESIDENTIAL PRESS OFFICE /KAYHAN OZER

When President Obama spoke Tuesday of the strikes on the Islamic State and al Qaeda in Syria, he prominently mentioned five partner nations from the Middle East: Saudi Arabia, the United Arab Emirates, Jordan, Bahrain, and Qatar. These countries had contributed militarily to the fight against extremists, he said, describing them as a "friends and partners."

The message was clear: This military action was not unilateral. Instead, it was supported by Muslim-majority states, with the coalition against Islamic State so strong it could bring together Persian Gulf states which had previously been at odds.

There was clearly one big name missing, however. Turkey is a major U.S. ally in the Middle East and a NATO member with a strong military. Perhaps even more importantly, it shares a long border with both Syria and Iraq. Despite these factors, there has been no hint of Turkish involvement in the strikes from Washington or Ankara.

That Turkey is not taking part in the strikes will not come as a total surprise. When Secretary of State John F. Kerry headed to Turkey earlier this month to rally support for broader strikes against Islamic State, the response was lukewarm. Turkish officials made it clear that they did not want Turkish air bases used for staging any strikes – and they certainly would not be taking part in any attacks themselves.

Turkey had an obvious reason to be cautious. In June, the Islamic State raided the Turkish consulate in the Iraqi city of Mosul. Forty-nine Turkish citizens had been taken hostage and the Turkish government feared what would happen to them if the extremist group was provoked. "Our hands and arms are tied because of the hostages," one unnamed Turkish official told Agence France-Presse news agency as Kerry made his case.

This weekend, however, the situation changed. Turkey secured the release of all 49 hostages. It was a cause for celebration, but circumstances were surprising: Turkey claimed no shots were fired, no ransom was paid, and no prisoners were exchanged.

To many, that just seemed too good to be true: the Islamic State had shown horrific brutality to other hostages and the Turkish citizens would likely hold high value as a bargaining chip. “There are some very legitimate and unanswered questions about how this happened," Sinan Ulgen, a former Turkish diplomat who now chairs the Istanbul-based Centre for Economics and Foreign Policy Studies, told the Associated Press.

Other factors also muddied the water further. As The Post's Anthony Faiola and Souad Mekhennet reported earlier this year, in the first few years of the Syrian war the Turkish government had adopted a somewhat laisse faire attitude to Islamist groups crossing into Syria, which in turn lead to a sizable Islamist presence in Turkish border towns. Turkey has since cracked down, but it may be too late: Numerous reports say that certain neighborhoods in Istanbul, Turkey's largest city, have become hotbeds of Islamic State support. Turkish officials now estimate that more than 1,000 Turkish citizens are fighting for the Islamic State.

Turkey also has a small number of troops in Syria guarding the Tomb of Suleyman Shah, an important figure in Ottoman history, at present. The tomb is considered a sovereign exclave of Turkey, yet is situated in Aleppo not far from significant fighting. Ankara may well be concerned that the exclave could be overrun by Islamic State fighters with relative ease. "The situation is a delicate if not impossible one for Ankara," Henri J. Barkey, a professor of International Relations at Lehigh University, wrote recently for Foreign Policy, "as the only way to resupply this small contingent of troops is by reaching some sort of understanding with the jihadist group."

Then there's the intertwined issue of refugees and Kurds. This weekend, some 150,000 Syrian Kurds crossed into Turkey, fleeing the Islamic State. Turkey would appear to have a lot to lose from the Islamic State displacing the Kurds and capturing Syrian land right up to the Turkish border, but Ankara appears to have taken little action: Syrian Kurds say that they are actively preventing Turkish Kurdish fighters from traveling into Syria to help them fight.

Ankara's position has clearly been complicated by its fraught relationship with the Turkish Kurds. The People's Protection Units, known by the acronym YPG, have been one of the strongest forces fighting against Islamic State, yet they are linked to the Kurdistan Worker's Party, or PKK, the separatist guerrilla group that has waged a Kurdish insurgency against the Turkish state for decades. Both Ankarra and Washington consider the PKK a terrorist organization.

Many observers suspect that Ankara finds it easier to tolerate the Islamic State's rampage in Syria than cooperate with Kurdish groups like the PKK or YPG. "Turkey is preventing, not only PKK, but all Kurdish men from entering Syria,” Redur Xelil, a YPG spokesman, told The Post's Rebecca Collard at the weekend. “The reality is that Turkey is siding with ISIS,” he added, using an acronym for an old Islamic State name.

Speaking at a Council of Foreign Relations event in New York City, President Recep Tayyip Erdogan hit back at claims Turkey supported Islamic State. However, his response may have also revealed his views on cooperation with Turkish Kurdish groups. "Turkey has fought terrorism for many years," he said. "We have paid a heavy price in that process. And we were on our own in that effort, and as such -- as a country, Turkey can never support any terrorist organization."

Turkey may have other reasons for not wanting to join in the airstrikes. The most simple of them all is that it might just not think its a good strategy: Remember, Turkey refused to cooperate during the U.S.-led Invasion of Iraq in 2002. Ankara could well consider that a good decision in hindsight.

For the United States, however, the hope is that Turkey will find a way past these issues and get on board: If nothing else, the use of air bases in Turkey would make strikes far easier. And speaking at a U.N. Global Counterterror meeting on Tuesday, Kerry did seem convinced Turkey could still be counted on to help the "friends and partners" against the Islamic State.

"Turkey is very much part of this coalition, and Turkey will be very engaged on the front lines of this effort," Kerry said. "But clearly, Turkey had an initial challenge with respect to its hostages, and that being resolved now, Turkey is ready to conduct additional efforts along with the rest of us in order to guarantee success. And we’re very grateful to Turkey for that willingness."

Anne Gearan contributed reporting to this post.