BEIRUT (Reuters) - U.S.-backed militias in Syria have detained senior foreign Islamic State leaders in months of fighting for Raqqa, but it is not yet clear if they will be repatriated after facing trial, a spokesman said on Thursday.  We have foreign emirs ... from all around the world,  Talal Silo of the SDF told Reuters.  They were captured in special operations, and some of them turned themselves in to our forces.  The Syrian Democratic Forces (SDF), an alliance of Kurdish and Arab militias, declared victory this week in Raqqa, raising flags over the last Islamic State positions in the city.  The fall of Raqqa marked a potent symbol of the jihadist movement s collapsing fortunes. Islamic State militants used the city as a planning and operations center for its warfare in the Middle East and its string of attacks overseas. The United States has said Raqqa served as a hub for attacks abroad. In November 2015, after militants killed more than 130 people in Paris, France said it launched air strikes on Islamic State targets inside Raqqa. Silo declined to say how many high-ranking, foreign Islamic State prisoners were in detention, but said SDF intelligence was interrogating them.   There are prisons dedicated just for Daesh,  he added, using the Arabic acronym for Islamic State.  We don t put them with the regular prisoners.    They are being investigated, and will be presented to the courts. We have an independent judicial system that will try them, all of them,  he said.  After the trials, it remained unclear if the SDF would hand over the fighters to their countries or whether the foreign states would accept to take them back, he said.   It depends on the situation between us and the (foreign) states,  Silo said.  There may be an agreement ... there may be consent to handing them over, and there may not be.  With air strikes and special forces from the U.S.-led coalition, the Kurdish-led SDF had been fighting since June inside Raqqa, after months of battles to encircle the city. Raqqa was the first major city Islamic State seized in early 2014, before its series of rapid victories in Iraq and Syria brought millions of people under the rule of its self-declared caliphate, which passed laws and issued passports and money. 