"Once we get those patrols going along the line of contact and we take out the rest of the caliphate, our goal would be to set up local security elements that prevent the return of [IS] while at the same time diplomatically supporting… the Geneva process," Mattis said on Monday.

Earlier on Monday, National Security Advisor John Bolton, however, said at the United Nations General Assembly that US military will stay in the country.

Mattis, however, noted he and Bolton were "on the same sheet of music," when it comes to Syrian issue.

Reporter’s code: 50101