Persistent attacks on Americans in Iraq are being carried out by regional bands that include Saddam Hussein loyalists and disgruntled ex-soldiers but have not formed into a national network, an Iraqi police official says. The U.S. military insisted the resistance is the "last dying breath" of enemy forces.

The violence — most recently the killing of another U.S. soldier on Wednesday — has underscored the volatility of a U.S.-led occupation that's been forced to concentrate on security over reconstruction and has raised fears of a guerrilla war.

Iraqi security officials working with the Americans said regional leaders are directing the attacks by people still loyal to Saddam, former soldiers, Sunni Muslim radicals and non-Iraqi "holy warriors."

With U.S. forces carrying out a large sweep to put down resistance, Defense Secretary Donald H. Rumsfeld said American troops are "rooting out pockets of dead-enders." He told reporters at the Pentagon that groups of 10 to 20 people were behind the attacks on soldiers, not "large military formations."

The commander of the 4th Infantry Division, Maj. Gen. Ray Odierno, called the losses "militarily insignificant" and said troops had captured local leaders of new fanatic groups with names like "The New Return" and "The Snake Party" — bands that are more like street gangs than organized paramilitaries.

More than 50 U.S. soldiers have been killed in Iraq, either in attacks or accidents, since major combat was officially declared over on May 1.

On Wednesday, gunmen killed one American soldier and wounded another in a hit-and-run shooting at a Baghdad propane gas station. Also in Baghdad, U.S. troops fired on a demonstration by angry former soldiers, killing two protesters.

A senior Iraqi police official said each region has leaders coordinating the resistance, though a lack of communication has prevented them from forging a united front.

Most recent attacks in and around Baghdad are the work of former members of Saddam's security forces who lost their jobs, the official said, speaking on condition of anonymity.

North and west of Baghdad, in the so-called Sunni triangle where anti-U.S. sentiment runs high, religious extremists are carrying out attacks, the official said.

Brig. Ahmad Kazem Ibrahim, a senior Iraqi police official in Baghdad, blamed former members of Saddam's Baath party for the attacks on Americans, saying "they want to recapture their past and revive their glory."

U.S. military spokesman Capt. John Morgan said "it may be true" that the attacks are being coordinated regionally, but said it's more likely that they're localized acts committed by former regime members taking "their last dying breath."

He said he doesn't want to speculate on what might happen if Iraq's resistance ever organized itself nationally, saying only that "we would act on it and deal with it."

The chief resistance group is the "Party of the Return," or Hizb-al-Awda, according to knowledgeable officials, who say they are the most organized.

The group consists of small, loosely organized cells in Baghdad, Basra, Mosul and other cities and each cell may have a few people up to perhaps two dozen — most Baath Party (search) officials or security officials from Saddam's regime, the officials said, speaking on condition of anonymity. They are cooperating with remnants of Saddam's Fedayeen (search), the officials said.

Other anti-American groups, including the Iraqi Resistance Brigades (search) and the General Command of the Iraqi Armed Resistance and Liberation Forces are thought to be very small and not terribly capable, the officials said.

Non-Iraqi fighters, perhaps with links to Usama bin Laden's Al Qaeda network, are also suspected in the anti-American attacks. Pentagon and intelligence officials say these include Saudis, Yemenis, Syrians and Africans motivated primarily by anti-U.S. Islamic ideology rather than support for Saddam.

Odierno, speaking to Pentagon reporters from Iraq, said Islamic fundamentalists are among attackers, as are "just plain Iraqis who are poor" and being paid a bounty to injure or kill Americans. He said he didn't know the amount because figures given during interrogations of prisoners had varied.

But he said American forces are making progress against Iraqi resistance.

"We are seeing military activity throughout our zone, but I really qualify it is as militarily insignificant," he said, though he added, "I will never downplay Americans being killed in combat. It is a very significant sacrifice, especially for their families."

As an example of progress, troops on Wednesday rounded up 50 more people in Tikrit (search) tied to Saddam's security or paramilitary groups, Odierno said.

The United States has begun a crackdown to crush the resistance, arresting more than 400 people this week alone. Its tactics — rousing people from their beds in the dead of night, whisking them away blindfolded — is fueling Iraqi anger, possibly preparing the stage for more attacks.

"They [the Americans] are worse than Saddam," said Khalid Ibrahim, a 50-year-old driver who was among two dozen people arrested and interrogated outside a mosque in Baghdad last weekend and released after five hours.

Iraqis and Americans fear that the cycle of strike and counter-strike is diverting U.S. attention away from rebuilding postwar Iraq.

L. Paul Bremer (search), the top U.S. official in Iraq, banned the Baath Party last month, prohibiting any members of its upper three echelons from working in any Iraqi ministry. The Iraqi military has also been dismissed.

Wednesday's demonstration outside Saddam's former presidential compound, now the headquarters of the U.S.-led administration, was by former Iraqi soldiers seeking jobs and back pay. Two Iraqis were shot dead when protesters starting throwing rocks.

Former Sgt. Mohammed Jafer Hassan, a demonstrator, predicted violence against Americans will increase.

"We have weapons including RPGs [rocket propelled grenades]," he said. "We may use them if our demands are not met."