Obama: not possible to know duration of action against Islamic State

WASHINGTON (Reuters) - U.S. President Barack Obama on Tuesday said it was not possible to know how long U.S.-led operations against Islamic State militants in Syria and Iraq will last as the U.S. military launched the first strikes against the militant group in Syria. In a letter to Congress following the air strikes, Obama said: "It is not possible to know the duration of these deployments and operations. I will continue to direct such additional measures as necessary to protect and secure U.S. citizens and our interests against the threat posed by ISIL," using another name for Islamic State. (Reporting by Susan Heavey; Editing by Doina Chiacu)