The United States has warned Iran not to interfere in its neighbour's affairs.
The warning came a day after members of the Iraqi Shi'ite community demonstrated their new-found religious freedom during a Shi'ite festival, the first since the collapse of Saddam Hussein's regime.
As Shi'ite pilgrims thronged the streets of the holy city of Kerbala for a religious festival, Washington, apparently nervous that Iraq's religous majority might take their lead from predominantly Shi'ite Iran, warned Tehran against interfering.
"We've made clear to Iran that we would oppose any outside interference in Iraq's road to democracy," said White House spokesman Mr Ari Fleischer. "Infiltration of agents to destabilise the Shi'ite population would clearly fall into that category".
The United States believes Iranian-trained agents have crossed into southern Iraq since the fall of Saddam and are working to advance Iranian interests.
Elsewhere, US forces claimed to have rounded up four more alleged members of Saddam Hussein's ruling elite.
Gen. Zuhayr Talib Abd al Sattar al Naqib, Saddam's alleged chief of military intelligence, gave himself up in Baghdad yesterday. US special forces captured Salim Sa'id Khalaf Al-Jumayli, the alleged former head of the Iraqi Intelligence Service's American desk.
In an interview with the Los Angeles Timesbefore he turned himself in to US soldiers, Gen Naqib said he was a military man who had simply followed orders. He denied he had done anything that could be counted as a crime against humanity.
The US military also said Muzahim Sa'b Hassan al-Tikriti, Air Defence Force commander and Number 10 on the wanted list, "is under coalition control" but gave no further details.
The former Iraqi minister of trade, Muhammad Mahdi al-Salih, is also in US custody, bringing to 11 the number of Iraqis on the US most-wanted list to surrender or be captured. Three others are dead.