Brussels, Belgium ? Defense Secretary Robert Gates said Monday that new U.S. 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 said at NATO headquarters before flying to Kabul to meet with Afghan President Hamid Karzai and visit U.S. soldiers and commanders.

It was Gates’ first trip to Afghanistan since he took over for Donald Rumsfeld last month; he had said several times recently that he is worried that U.S. 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 Iran’s perception of U.S. 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 U.S. forces in the area. The Pentagon has not said exactly where the Patriots will be based.

The second aircraft carrier gives the U.S. more flexibility and serves as a reminder of U.S. firepower.

Laying out his concerns about Iran, Gates cited Iranian support for the radical Hezbollah movement in Lebanon. He also asserted that the Iranians “are doing nothing to be constructive in Iraq at this point.” Other U.S. officials have accused Iran of providing sophisticated bomb-making materials to insurgent groups in Iraq.

Gates said that as recently as 2004 the Iranians were “actually doing some things to be helpful” in Iraq, at a time when they felt concern at the presence of U.S. troops on their western and eastern borders, in Iraq and Afghanistan. At that point, he thought diplomatic dialogue would be useful.

“None of those conditions apply any longer,” Gates said, responding to questions about the reasoning behind the Pentagon’s decision to dispatch a the battle group and missile battalion to the Gulf area.

“My view is that when the Iranians are prepared to play a constructive role in dealing with some of these problems, then there might be opportunities for engagement,” he added.

Gates’ comment about Iran perceiving the U.S. military as bogged down in Iraq appeared to reflect a concern felt by many in the Pentagon in connection with deepening U.S. involvement in Iraq.