The US Navy has temporarily added a second aircraft carrier in the Gulf as a 'reminder' to Iran, but this was not an escalation of American forces in the region, US Defense Secretary Robert Gates said.

Speaking to reporters during a trip to Mexico, Gates flatly denied a suggestion that the presence of two US carriers in the Gulf could be a precursor to military action against Tehran.

'This deployment has been planned for a long time,' Gates said. 'I don't think we'll have two carriers there for a protracted period of time. So I don't see it as an escalation. I think it could be seen, though, as a reminder.'    

He declined to elaborate on his remarks and provided no details about the deployment.

Pentagon spokesman Geoff Morrell said the second carrier arrived in the Gulf on Tuesday to replace one on duty that was expected to depart the region in two days.

US Navy officials were not immediately available for comment.

News of the second carrier came amid simmering tension between the United States and Iran that has fed speculation about a possible US military strike.

Navy Adm Mike Mullen, chairman of the US Joint Chiefs of Staff, said last week that the Pentagon had military options it could consider against Tehran but stressed that the United States would continue to rely on diplomatic and economic methods to address its concerns.

Iran and the United States have repeatedly clashed over US claims that Tehran is pursuing nuclear arms and aiding Shi'ite militants in Iraq who have recently stepped up attacks on US-led coalition forces.

Tehran maintains it is pursuing a civilian nuclear energy program and blames violence in Iraq on the presence of about 160,000 US forces. - Reuters