US Secretary of Defense Robert Gates warned Tuesday of "pretty dramatic" consequences of not having an accord governing the presence of US troops in Iraq.

"The consequences of not having a SOFA (Status of Forces Agreement) and of not having a renewed UN authorization are pretty dramatic in terms of consequences for our actions," said Gates, speaking to members of three news agencies including AFP.

A status of forces agreement would replace the current UN mandate — which expires December 31 — as the legal basis for the US military presence in Iraq.

"Clearly, the clock is ticking," said Gates. "Clearly there is a need to keep moving just so that we don't run out of time."

According to Gates there are "only two alternatives: the SOFA or a renewed UN mandate, and going back to the UN at this point there is no assurance that you get a clean rollover," Gates said.