Leon Panetta arrived in Iraq on Sunday on his first trip there as US Defense Secretary, saying he would press Baghdad to decide on the future US military presence and to go after militants attacking US forces with Iranian rockets.

Panetta said that weapons supplied by Iran had become a “tremendous concern” for the United States in recent weeks in Iraq, where more American troops died in June in combat-related episodes than in any month since June 2008.

“We’re seeing more of those weapons going in from Iran, and they’ve really hurt us,” Panetta said before arriving to Baghdad, on an unannounced trip, from Helmand Province, in Afghanistan, where he met with American Marines and Afghan Army soldiers at Camp Dwyer, a sprawling military base and the site of a busy medieval hospital in the southern desert.

Panetta’s comments, made a day before he was to meet with the Iraqi Prime Minister, Nuri Kamal al-Maliki, were aimed at urging the Iraqi military to take stronger action against Shiite militias.

“The key right now is to make sure that we do everything possible to ensure that the Iraqis within their own country are doing what they can to stop the flow of those weapons and to stop the Shia from using them,” Panetta said.

Iraq did begin a crackdown on Shiite militias in the south in recent days, but the American military would like the Iraqis to do more.

The United States is scheduled to withdraw all of its remaining 46,000 troops from Iraq by end of this year, under the terms of a bilateral security pact despite US and Iraqi military concerns about expected gaps in security.