Defense Secretary Robert Gates says the latest move to add a second U.S. aircraft carrier in the Persian Gulf could serve as a "reminder" to Iran. But he says it's not an escalation of force.

Gates is insisting that the U.S. is not laying the groundwork for a strike against Tehran. But he says Iran is giving the Taliban in Afghanistan a continuing flow of support.

Gates spoke to reporters in Mexico City after meeting with Mexican leaders. His comments come as U.S. officials continue to complain that Iran is increasing its efforts to supply weapons and training to militants in Iraq.