In this restive city and across Iraq's Sunni heartland, many Saddam loyalists refuse to believe that a disheveled and bearded man in U.S. captivity is their ousted leader, whose 23-year rule boosted their position as the country's political elite.

Saddam Hussein's capture Saturday touched off a wave of clashes between insurgents and U.S. troops and their Iraqi allies in Fallujah (search), Samarra, Tikrit (search) and Mosul.

The cities straddle areas dominated by Sunni Arabs, who had held the reins of power over the country's Shiite Muslim majority until the Iraqi leader was ousted in the U.S.-led war.

The attacks — along with pro-Saddam protests in Sunni areas of Baghdad and other cities — appear aimed at spoiling the major victory scored by the United States when it nabbed the former dictator in a hideout near his hometown of Tikrit.

Sunni defiance showed itself in attitudes as well as actions.

"It is someone wearing a Saddam mask," volunteered Waleed Ibrahim, a 25-year-old tire repairman in Fallujah, 30 miles west of Baghdad. "It is a trick to help President Bush get re-elected."

Minutes before he spoke, U.S. tanks, Bradley fighting vehicles and Humvees carrying dozens of troops roared into the city in a show of force after a night of clashes with Saddam loyalists.

Jet-fighters screamed overhead and two helicopters dived and swerved at low altitude.

"The coalition forces have arrested Saddam Hussein. Reports that it is a Saddam double are false," declared a voice on a loudspeaker fixed on one U.S. Humvee in Fallujah on Tuesday.

"The old regime will never come back. This is the end of the Baath party (search)," said the voice, speaking in Arabic.

"Whoever carries a weapon will be killed," the voice said.

"This is terrorism," said Hamed Ali, a shopkeeper, who recounted how jets buzzed the city for most of Monday night. "Even children were cursing the Americans."

The incredulity at news of Saddam's capture was only the latest in a series of reactions that have defined the mood among some Sunnis since Saddam's ouster eight months ago.

Iraq's Sunnis greeted news of the July killings of Saddam's sons Uday and Qusay with similar disbelief. They often dismiss evidence of crimes against humanity committed by Saddam's 1979-2003 regime as fabrications of the United States, Iran and their Iraqi allies.

The defiance is partly a reaction to the loss of prestige and privileges in a new political order that restored the rights of the country's Shiite majority and large Kurdish minority — groups long victimized by the Sunni Arab minority. Between them, they account for about 80 percent of Iraq's 25 million people.

In Tikrit, Saddam loyalists tried to stage a demonstration in support of the former dictator Tuesday, but neither the city's U.S.-backed governor nor the U.S. military were prepared to stand by and watch.

"Any demonstration against the government or the coalition forces will be fired upon," the governor, Hussein al-Jaburi, said on a loudspeaker mounted on a U.S. military vehicle.

"They will not be allowed to go around kissing pictures of Saddam," said Lt. Col. Steven Russell of the Tikrit-based 4th Infantry Division. "We cannot hand out lollipops in this city. It does not work here."

Earlier Tuesday, Russell had a stern warning for the organizer of a pro-Saddam march: "If our ears and eyes see you organizing demonstrations or anti-coalition acts, you will be in jail for a very long time."

In Fallujah, several hundred armed protesters carrying Saddam portraits stormed the mayor's office Monday, forcing policemen to flee to the nearby police headquarters, according to witnesses. U.S. troops backed by tanks and Bradley fighting vehicles came to their rescue but were attacked by insurgents. They fired back, killing one guerrilla.

U.S. military sources in the area said insurgents Tuesday attacked an Iraqi train ferrying military supplies with rocket-propelled grenades, setting three of its cars ablaze.