Sending a second aircraft carrier to the Persian Gulf could serve as a "reminder" to Iran, but he said it is not an escalation of force, said US Defense Secretary Robert Gates Tuesday. Speaking to reporters after meeting with Mexican leaders, Gates said heightening US criticism of Iran and its support for terrorist groups is not a signal that the administration is laying the groundwork for a strike against Teheran. Still, he said Iran continues to back the Taliban in Afghanistan. "I do not have a sense at this point of a significant increase in Iranian support for the Taliban and others opposing the government in Afghanistan," Gates said. "There is, as best I can tell, a continuing flow, but I would still characterize it as relatively modest."