"Reminder" to Iran,

MEXICO CITY — Defense Secretary Robert Gates said Tuesday that sending a second U.S. aircraft carrier to the Persian Gulf could serve as a "reminder" to Iran, but he said it's not an escalation of force.

Speaking to reporters after meeting with Mexican leaders, Gates said heightening U.S. criticism of Iran and its support for terror groups is not a signal that the administration is laying the groundwork for a strike against Tehran.

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."

His comments contrasted with those from Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, who said last week that he had not seen any new signs of Iranian support for the Taliban.

Gates played down the addition of a second carrier to the Gulf, saying that the number of ships there rises and falls continuously. He said he doesn't expect there to two carriers there for a long time.

Asked if the carrier move went hand in hand with the rising U.S. rhetoric against Iran, Gates said, "I don't see it as an escalation. I think it could be seen, though, as a reminder."

In the past, military officials have said that beefing up the Navy's presence in the Gulf was a way to show that that the U.S. remains committed to the region. And they have acknowledged it also serves as a show of force for other countries there, such as Iran.