WASHINGTON - US President Barack Obama on Tuesday said it was not possible to know how long US-led operations against Islamic State militants in Syria and Iraq will last as the US 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 US citizens and our interests against the threat posed by ISIL,' using another name for Islamic State.
