"The American ambassador is the gate through which terrorism enters Iraq," says a banner hanging from the fence surrounding the tombs of Imam Hussein and Imam Abbas, among the most revered martyrs of the Shiite Muslim faith.
For three years, most of Iraq's Shiites welcomed -- or at least tolerated -- the U.S. presence here. In the weeks immediately after the American-led invasion, the mothers and sisters of Saddam Hussein's Shiite victims clutched clumps of dried earth as they wept over mass graves and thanked God for ending their oppression.
The Shiite acceptance of an American presence allowed troops to concentrate on putting down the insurgency in western Iraq, which is led by Sunni Muslim Arabs. With the exception of an uprising in mid-2004 by followers of radical cleric Muqtada Sadr, the south has been relatively quiet and peaceful under the sway of Grand Ayatollah Ali Sistani.
But now the mood has shifted. Perceived American missteps, a torrent of anti-U.S. propaganda and a recently emboldened Shiite sense of political prowess have coalesced to make the south a fertile breeding ground for antagonism toward America's presence.
The change has weakened the Bush administration's position and dimmed its hopes that Iraq's Shiites would counter the vehement anti-Americanism of their coreligionists across the border in Iran.
"There is an anger," said Jaffar Mohammed Asadi, spokesman for Ayatollah Mohammed Taqi Modaressi, a moderate and well-regarded cleric known more for his attempts to boost business in Karbala than for fiery anti-American speeches.
"You can hear it in the slogans at Friday prayers: 'Death to America,' " he said. "They're burning American flags. They're saying, 'The Americans won't leave except by the funerals of their sons.' "
Several factors have combined to produce that Shiite fury.
Many Shiites think the U.S. betrayed them in 1991 when then-President George H.W. Bush called on Iraqis to rise up against Hussein but then took no action as the dictator mowed down an uprising in the south.
Moreover, nationalism is a strong current among Iraqi Shiites, and analysts say their anti-Western attitudes were sure to surface some day.
"We had a lot of grace period," said Graham E. Fuller, a former Mideast-based CIA operative now writing books about the region. "But essentially, no group in Iraq that aspires to rule with legitimacy can act in a way perceived as being pro-American."
Above all, however, the new Shiite attitude reflects the changed political reality of Iraq's south: Once the Shiites were weak; now they have power. Many say they no longer need the Americans.
In and around Karbala and Najaf -- the southern Iraqi cities that house the holiest shrines of Shiite Islam -- dozens of checkpoints are staffed by Shiite police officers and soldiers. The security has made the south much safer than Baghdad or heavily Sunni provinces. As U.S. forces struggle to recruit police officers and soldiers in Sunni areas, police in the southern Iraqi province of Muthanna on Wednesday proudly announced that they had busted a ring of drug dealers after a two-hour shootout.
"We agreed with Americans only at the point of removing Saddam Hussein," said Sheik Abu Mohammed Baghdadi, a cleric in Najaf who is close to Sistani. "The relationship ended at that point."
U.S. officials point to yet another factor in the souring of relations: what they describe as an intense propaganda campaign, some of which emanates from Iran, that seeks to paint American policy in the ugliest terms.
In interview after interview in Najaf and Karbala, Shiites adhered to a version of current events that magnified corruption and torture cases into pervasive abuses by the Americans and depicted U.S. Ambassador Zalmay Khalilzad, a Sunni born in Afghanistan, as anti-Shiite.
"We need to do a better job of explaining what we're doing, and some people are intentionally trying to mislead," Khalilzad said in a recent interview.