The Obama administration had pressed Turkey for a larger role against the extremists, and a senior US official confirmed today that Ankara had agreed to train and moderate Syrian rebels on Turkish soil.
A Turkish government official today said that Turkey put the number at 4,000 opposition fighters and said they would be screened by Turkish intelligence.
US Defense Secretary Chuck Hagel, who has been traveling in South America, has said the US wanted access to the Turkish air bases, including one at Incirlik in southern Turkey, from which to launch strikes against the Islamic militants.
Beyond the training and bases, there are other issues the US hopes Turkey will agree to. US officials have not said what all of those would be because discussions are continuing.
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The militants have taken over large swaths of Iraq and Syria and driven refugees into Turkey.
President Barack Obama's national security adviser, Susan Rice, made clear that the US has not asked "the Turks to send ground forces of their own into Syria."
"So Turkey has many ways it can contribute," Rice told NBC's "Meet the Press."
Turkey and other American allies are pressing the US to create a no-fly zone inside Syrian territory, and seeking creation of a secure buffer on the Syrian side of the border with Turkey.
A "safe zone" would require Americans and their partners to protect ground territory and patrol the sky, meaning enforcement of a no-fly area.
Gen. Martin Dempsey, the chairman of the Joint Chiefs of Staff, has estimated it would require hundreds of US aircraft and cost as much as USD 1 billion a month to maintain an area in Syria safe from attacks by the Islamic State group and Syria's air force, with no assurance of a change in battlefield momentum toward ending the Syrian civil war.