An aide to Iraq's most prominent Shiite (search) cleric on Friday branded the U.S. formula for transferring power a "hasty agreement" aimed at boosting President Bush's re-election campaign.

Doubts over the American plan for transferring power to Iraqi hands by July 1 have loomed over the U.S.-led occupation this week, with the Americans pointing to sporadic violence as evidence the country is not ready for direct elections.

The bloodshed persisted in Baghdad Friday, as a roadside bomb missed American troops but killed one Iraqi boy and wounded three others as they played soccer along a busy street. The U.S. command also announced an investigation into alleged abuse of Iraqi prisoners.

Grand Ayatollah Ali al-Husseini al-Sistani (search), the country's most influential Shiite Muslim leader, has demanded that members of a new provisional legislature be chosen by voters. The Americans want them selected by regional caucuses.

U.S. officials insist al-Sistani's demand for elections is unfeasible given Iraq's security situation. Many Shiites suspect the Americans simply want to manipulate the caucuses to make sure favored Iraqis win seats.

In Washington, the U.S. administrator for Iraq, said the United States will revise its plan to create self-rule in Iraq, but he rejected postponement of a June 30 deadline for ending the occupation and handing over power.

"The Iraqi people are anxious to get sovereignty back, and we are not anxious to extend our period of occupation," the administrator, L. Paul Bremer (search), said after conferring at the White House with Bush and senior U.S. officials.

To underscore their demands, Shiite clerics mustered up to 30,000 protesters in the streets of this southern city Thursday. Shiites comprise about 60 percent of Iraq's 25 million people.

A day after the demonstration, al-Sistani's representative in Basra sent a letter to Bush and British Prime Minister Tony Blair (search) questioning the sincerity of the power transfer plan.

"Many political analysts are saying that the purpose of the hasty agreement ... was propaganda for your re-election campaign, especially after what your country has suffered because of military losses in Iraq," the letter by cleric Ali Abdul Hakim al-Safi (search) said.

"All we are looking for and want is that our rights not be ignored and the rights of others not be ignored," the letter added. "We know that all the excuses you used to hinder the elections are not based in reality."

It said al-Sistani's election demand "represents the aspiration of the Iraqi people without distinguishing between different sectors and nationalities, because everybody is a son of Iraq and they are all equal."

Mohammed Baqir al-Mehri, al-Sistani's representative in Kuwait, warned on Abu Dhabi television Thursday that al-Sistani would issue a fatwa, or religious edict, declaring the U.S. plan illegitimate if the Americans refuse his demand.

Bremer meets with U.N. Secretary-General Kofi Annan and the U.S.-appointed Iraq Governing Council on Monday. U.S. officials hope Annan will agree that early elections are unreasonable.

"There are a number of ways in which these kinds of selections can go forward," Bremer said Friday in Washington. "We've always said we are willing to consider refinements and that is something we will be willing to discuss at the appropriate time."

In Baghdad, the commander of coalition military forces said the forthcoming transfer of power to Iraqis offered an opportunity for insurgents to lay down their arms and help rebuild the country.

"The timing is perfect for the anti-coalition forces and former regime elements to make a decision that it is time to embrace the future," Lt. Gen. Ricardo Sanchez said. "The former regime is never going to come back."

Later, U.S. officials said the military ordered a criminal investigation into alleged prisoner abuse at detention centers in Baghdad. The officials declined to provide other details, saying release of information could hinder the inquiry.

Earlier this month, three U.S. Army reservists were discharged for abuse of prisoners at a detention center in southern Iraq. In late December, Brig. Gen. Ennis Whitehead III determined the three had kicked prisoners or encouraged others to do so on May 12. Lt. Col. Allen B. West, a battalion commander in the 4th Infantry Division, was allowed to resign from the Army after he admitted firing a weapon near a detainee.