Kerry met Turkish leaders to try to secure backing for U.S.-led action against Islamic State militants, but Ankara's reluctance to play a frontline role highlighted the difficulty of building a willing coalition for a complex military campaign in the heart of the Middle East.
As he tours the region to gather support for President Barack Obama's plan to strike both sides of the Syrian-Iraqi frontier to defeat Islamic State Sunni fighters, Kerry said Shi'ite Iran should have no role in talks on how to go about it.
Accusing Iran of being "a state sponsor of terror” and backing Syria’s brutal regime, Kerry said it would be inappropriate for Iranian officials to join an Iraq conference in Paris on Monday to discuss how to curb a jihadist movement that has seized a third of both Iraq and Syria. Tehran has described the coalition as "shrouded in serious ambiguities".
"Under the circumstances, at this moment in time, it would not be right for any number of reasons. It would not be appropriate given the many other issues that are on the table in Syria and elsewhere," he told a news conference in the Turkish capital Ankara.
Faced with disparate interests and goals among the region’s often squabbling nations, Kerry said it was too early to say publicly what individual countries were prepared to do in a broad front to cut off funds to the militants, encourage local opposition and provide humanitarian aid.
Kerry won backing on Thursday for a "coordinated military campaign" against Islamic State from 10 Arab countries - Egypt, Iraq, Jordan, Lebanon and six Gulf states including rich rivals Saudi Arabia and Qatar. (Full Story)
But it remains far from clear what role individual nations will play. While he confirmed France's commitment to use military force in Iraq, he declined to say whether France would join strikes in Syria.
That follows conflicting reports in key ally Britain over its potential role, with Prime Minister David Cameron on Thursday saying he has not ruled out military action in Syria after his foreign secretary said Britain would not take part in any airstrikes there.
"It is entirely premature and frankly inappropriate at this point in time to start laying out one country by one country what individual nations are going to do," said Kerry, who travels to Cairo on Saturday, adding that building a coalition would take time.
"I'm comfortable that this will be a broad-based coalition with Arab nations, European nations, the United States, others," he said. "At the appropriate time, every role will be laid out in detail."
Turkey, which has the second-largest armed forces in the NATO military alliance after the United States and hosts a major U.S. Air Force base at Incirlik in its south, has so far conspicuously avoided committing to any military campaign.
Prime Minister Ahmet Davutoglu, who did not join the news conference with Kerry, said in a live interview on Turkish television hours after their meeting that U.S. action in Iraq would not be enough on its own to bring political stability.
"It is necessary, but it is not enough to establish order," he told the Kanal 24 TV station.
U.S. officials played down hopes of persuading Ankara to take a significant role in any military involvement, saying Friday's talks were focused on issues including Turkey's efforts to stem the flow of foreign fighters crossing its territory and its role in providing humanitarian assistance.
"The Turks have played an extraordinary role on humanitarian aspects of the situation ... and they are going to play and have been playing a pivotal role in our efforts to crack down on foreign fighter facilitation and counter terrorist finance," a senior U.S. State Department official said before the talks.

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