At least 23 American soldiers have been killed in Iraq since Friday as U.S. and coalition forces continue to battle Sunni militants in Fallujah and Shiite militants in southern Iraq. The upsurge in fighting comes more than a year after U.S. and coalition forces toppled Saddam Hussein and less than three months before the transfer of sovereignty to the Iraqi people. Just how serious a threat do these militants pose to a free Iraq? VOA?s Serena Parker reports from Washington.

The United States suffered another bloody weekend in Iraq as fighting between coalition forces and Sunni and Shiite militants claimed the lives of more than two dozen American soldiers and hundreds of Iraqis, leading many to question the Bush Administration?s planning for post-war Iraq.

?I think they did make a grievous error in underestimating the opposition,? says Steve Yetiv, associate professor of political science at Old Dominion University in Virginia. According to Mr. Yetiv the U.S. military was brilliant at launching a conventional military attack but has not been effective in safeguarding its progress since then. If they don?t get a handle on the Shiite unrest, the coalition may be in for a potentially threatening insurrection.

?They need to neutralize Moqtada al-Sadr and not just neutralize him but make a statement in his neutralization that this kind of wanton insurrection is intolerable and cannot succeed,? he says. ?If they don?t make that statement, then they may be facing a Pandora?s Box (a source of extensive, unforeseen troubles). And to make that statement I think you need more troops. You can?t just have a troop structure that is designed for a country that you thought would be largely civil.?

For over a year, American forces have been fighting insurgents in the area north of Baghdad known as the Sunni Triangle. After four American military contractors were killed and their bodies mutilated, U.S. Marines cordoned off the city of Fallujah and have been fighting militants. A tentative cease-fire was still underway Monday as pro-U.S. Iraqi politicians met with Fallujah city officials.

At the same time the violence swelled in the Sunni Triangle, coalition forces chose to confront Moqtada al-Sadr, the 31-year-old, fiercely anti-American Shiite cleric who has a strong following among young, impoverished Iraqi Shia. On March 28 coalition forces shut down his newspaper for inciting hatred and violence against U.S. forces. Sadr?s supporters quickly took to the streets. Violence erupted when members of the cleric?s private militia took over government buildings and police stations and engaged in gun battles with coalition forces. Men loyal to Mr. Al-Sadr remain holed up in the southern Iraqi holy cities of Karbala, Kufa and Najaf.

The U.S. military has vowed to re-take the cities and disarm the militia. The coalition forces also have an arrest warrant for Moqtada al-Sadr, but Graham Fuller, former vice chairman of the National Intelligence Council at the CIA, wonders if that will be enough to quell the Shia uprising.

?The capture or killing of Moqtada al-Sadr may on the one hand possibly quiet things down for a while,? he says. ?But I would argue that you can eliminate the person who at the moment represents the wing of radical Shiite thinking, but the radical wing of Shiite thinking is not going to go away simply because the leader is killed.?

Mosque loudspeakers in Baghdad have called for blood, medicine and food donations for Fallujah, and both Shiites and Sunnis are taking in thousands of refugees, according to media reports. But Graham Fuller says coalition forces have yet to confirm any military cooperation between Sunni and Shiite fighters.

?Of course, the ultimate nightmare for Washington would be if there were a Sunni-Shiite collaboration against the United States,? he says. ?I think that could well happen as the clock runs out on the June 30th date for the turnover. In other words, the U.S. presence every day becomes less relevant, and players naturally are jockeying for the moment when the United States does turn over the sovereignty.?

Mr. Fuller says we now see Moqtada al-Sadr jockeying for influence among the Shia. So far his support has been largely confined to Sadr City, a sprawling slum in Baghdad that is home to two million Shiites. His rival, Grand Ayatollah Ali al-Sistani, claims the allegiance of most of Iraq?s 14 million Shiites. According to Rachel Bronson, director of Middle East Studies at the Council on Foreign Relations in New York, Mr. Al-Sadr?s call to arms helps him broaden his support.

?In fact what we see is a power struggle right now where Moqtada al-Sadr sees this as his last chance to really widen his base,? she says. ?He doesn?t have the same kind of following as al-Sistani does. I think that?s clear by the number of people he can put out on the streets. Now al-Sistani is in a little bit of difficult position in that he doesn?t necessarily want to alienate the followers of Sadr. It?s not in his interest to alienate them and he?s trying to keep the Shia community somewhat unified. From his point of view, Moqtada al-Sadr is probably threatening the unity. So he?s walking a fine line as well.?

At the center of the power struggle between the two clerics is the future of Iraq. Mr. Al-Sadr wants the immediate withdrawal of occupation forces and aims to establish an Islamic theocracy akin to neighboring Iran?s. Whereas Ayatollah al-Sistani supports some form of Islamic democracy.

Steve Yetiv, of Old Dominion University in Virginia, says Mr. Al-Sadr?s radicalism will only serve to strengthen Ayatollah al-Sistani. ?One thing that surely is going to come out of this is that Grand Ayatollah Ali al-Sistani?s power has increased,? he says. ?The United States needs him more now also not only to not join in any uprising but also to isolate Moqtada al-Sadr, which is rather critical. So if anything comes out of this profoundly, it?s that al-Sistani?s power will increase and will remain increased for some time and therefore make it more likely that Iraq will look like what al-Sistani wants in the future than was just the case a few days ago.?

Ayatollah al-Sistani and other Shiites worry about the U.S. plan to transfer power to Iraqis. The Shiites, long suppressed under Saddam Hussein, want to make sure they are given their rightful place in Iraqi society where they constitute a majority. They are concerned that an interim government will lack the legitimacy to deliver to them their long-due political power.

Rachel Bronson of the Council on Foreign Relations says the challenge in Iraq is to put some structures into place to deal with the divisions within Iraqi society in a peaceful manner and avoid any kind of civil strife: ?The challenge has always been that when there was a transition to Iraqi sovereignty, as we?re expecting on June 30th, to have something in place where there are ways of working through differences, to have some sort of institutional structure to deal with the inevitable conflicts that will confront Iraqi society. Those structures aren?t in place yet. We haven?t put them in place, and I?m not sure that we have any plan for putting them in place in the future. That?s the kind of thing that worries me about what?s looming in Iraq?s future.?

Although President Bush conceded it had been a ?tough week? in Iraq, he insisted that the transfer of power to the Iraqis will proceed as planned and said he sees no need for more U.S. troops. However, General John Abizaid, chief of the U.S. Central Command, sounded a slightly less optimistic note: he said he might extend the combat tour of some U.S. forces and is considering bringing more troops to Iraq.