US Secretary of State John Kerry said on Friday he was comfortable that the United States would form a broad-based coalition to fight Islamic State militants but said it would not be appropriate for Iran to be involved in the efforts.Kerry has been touring the Middle East to build support for President Barack Obama's plan, announced on Wednesday, to strike both sides of the Syrian-Iraqi frontier to defeat Islamic State Sunni fighters that control swathes of both countries."I'm comfortable that this will be a broad-based coalition with Arab nations, European nations, the United States, others," Kerry said, speaking in Ankara after meeting Turkish leaders.He said France had publicly made clear its willingness to take action in Iraq and to use force but said it was too soon to say what role individual nations would play."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," Kerry told reporters."At the appropriate time, every role will be laid out in detail," he said.Turkey, a NATO member which shares long borders with both Syria and Iraq, is one of Washington's main allies in the region. But it has so far conspicuously avoided committing to the new military campaign.Turkish leaders were not present at Kerry's press conference in Ankara.On Thursday, Kerry won backing 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.The German government will not take part in air strikes proposed by the US against Islamic State militants, an aide to Chancellor Angela Merkel said on Friday."The stabilization of the region is of great concern to the German government but I can rule out participation in military air strikes," said Merkel's spokeswoman Christiane Wirtz.