Secretary of State Rex Tillerson has said that US troops will remain in Syria not just to fight terrorists but also to counter the power of Bashar al-Assad and his ally Iran. In a speech on the US strategy to help end Syria's seven-year civil war, Tillerson stressed that the mission of the US military is to destroy the Islamic State terror group and prevent its return. <br/><br/>But he also made it clear that the open-ended deployment is intended to help create enough stability for Syrians to be able to remove Assad from office and reject Iranian influence. <br/><br/>A total withdrawal of American personnel at this time would restore Assad to continue his brutal treatment against his own people, Tillerson told an audience at Stanford University.<br/><br/>A stable, unified, and independent Syria ultimately requires post-Assad leadership in order to be successful, he said. <br/><br/>The United States has deployed around 2,000 ground troops to Syria and its warplanes patrol over the east of the country, hunting remnants of the Islamic State group. <br/><br/>The US works with the Syrian Democratic Forces, a militia dominated by Kurdish fighters which Washington sees as a basis for a 30,000-strong border force to hold eastern Syria. <br/><br/>The departure of Assad through the UN-led Geneva process will create the conditions for a durable peace within Syria and security along the borders, Tillerson said.