These are the questions being asked of the United States after new pictures showed US special forces troops traveling with Kurdish forces on the front line against the Islamic State in Syria.

For some, it's an issue of semantics. When Barack Obama announced in April that he would send some 250 special forces troops to Syria to support anti-ISIS fighters, State Department spokesman John Kirby explained the distinction to bemused reporters thusly:

"When we talk about boots on the ground ... we are talking about conventional, large-scale ground troops that are designed to actually engage in, plan, coordinate, integrate and engage in combat operations on the ground as units," Kirby said. "We're not doing that. We've never done that in Iraq or in Syria, and we're not going to do it now." 

US special operations forces, he added, "are not ground troops in the sense that they are not conventional ground troops conducting combat operations on their own."