US Defense Secretary Robert Gates said Monday that new US military moves in the Persian Gulf were prompted in part by signals from Iran that it sees the United States as vulnerable in Iraq. "The Iranians clearly believe that we are tied down in Iraq, that they have the initiative, that they are in a position to press us in many ways," Gates told reporters at NATO headquarters before flying to Kabul to meet with Afghan President Hamid Karzai and to visit US soldiers and commanders. It was Gates' first trip to Afghanistan since he took over for Donald H. Rumsfeld last month; he had said several times recently that he is worried that US gains in stabilizing Afghanistan could be in jeopardy as the radical Taliban movement makes a comeback in some parts of the country, particularly the south. In Brussels, Gates indicated that Iran's perception of US vulnerability was part of the reason the Pentagon decided last week to send a second aircraft carrier battle group and a Patriot anti-missile battalion to the Gulf area. Patriots defend against shorter-range missiles of the type that Iran could use to target US forces in the area. The Pentagon has not said exactly where the Patriots will be based.