WASHINGTON (Reuters) - The U.S. Department of Defense will soon submit a plan to Congress on how to defeat Islamic State, a defense official said on Thursday, four days before a deadline.  The National Defense Authorization Act (NDAA), a defense policy bill President Barack Obama signed into law in November, required the administration to submit its strategy for defeating the militant group to lawmakers by Feb. 15. Republican congressional leaders said on Thursday they had had no indication that the report was imminent despite the short time remaining before the deadline. “We are aware of the report and are actively working with multiple interagency offices to complete this legal requirement per the NDAA and look forward to submitting the completed report to Congress in the near-term,” the Department of Defense official said on condition of anonymity, in an emailed statement. Paul Ryan, the Republican speaker of the House of Representatives, issued a statement earlier Thursday calling on Obama, a Democrat, to submit by Monday a “real, comprehensive strategy” for defeating Islamic State. The United States is leading a military campaign against the militant Islamist group, which has seized swathes of territory in Syria and Iraq. Republicans in Congress have sharply criticized Obama for failing to defeat Islamic State, saying he mistakenly underestimated the threat it posed, allowing it to gain strength. U.S. Defense Secretary Ash Carter started talks in Brussels on Thursday with more than two dozen defense ministers, pressing allies to contribute to the effort. 