Hundreds of thousands of people marched through the capital Sunday in a protest against the rampant kidnappings and violent crime that have tarnished the image of North America's biggest city.

The protest attracted vast numbers of middle- and upper-class citizens who ordinarily stay in their walled homes. Wearing white clothes and carrying signs that read "Enough!" business leaders, professors, lawyers and others turned out to pressure officials to increase efforts to curb crime.

Andres Manuel Lopez Obrador, Mexico City's mayor and a leading presidential candidate in the already heated 2006 campaign, has accused his political opponents of organizing the march to embarrass him and exaggerate the crime problem. But many protesters interviewed said they were fed up with crime that had personally harmed them.

"They assaulted me at gunpoint," said Emilio Carrera, 43, an industrial engineer, who was "express kidnapped," a common crime in which victims are held until captors withdraw money from the victim's ATM account. "They beat me, took my car, my wallet. It's a miracle I am still alive. I had a pistol for two hours right here," he said, pointing to his head.

Some marchers wore black ribbons or carried pictures of family members who died as a result of violent crime, and national news commentators characterized the protest as the biggest in years.

Many Mexican cities and towns do not have serious crime problems. But this metropolitan area of nearly 20 million is plagued by murders, assaults and kidnappings, as are Ciudad Juarez, Tijuana and other cities along the U.S-Mexican border.

Last week, one of Mexico's top law enforcement officials said lax U.S. gun-control laws that allow arms to be sold "as if they were candy" were contributing to Mexico's violence.

Because many people do not trust the police, much crime goes unreported, making an accurate assessment of the problem difficult. Police have repeatedly been found to be involved in kidnappings. According to surveys by private and business groups, Mexico has one of the highest kidnapping rates in the world, as well as one of the highest rates of ransom money paid to kidnappers.

Front-page news stories of horrific kidnappings and of their victims -- including two brothers recently killed and dumped in a garbage bin after their family paid the ransom -- have become commonplace in recent weeks. Economic analysts here say they are worried that that image is hurting Mexican tourism, scaring off foreign investment and spurring many in the upper classes to move abroad.

Scores of civic groups organized Sunday's march, including a nonprofit group called the Committee for the Defense of the Users of Public Transportation. While many wealthy people travel with bodyguards and chauffeurs, most people ride the subway and city buses, where robberies and assaults are not uncommon.

"Because of the lack of attention to this security problem, people die," said Dahlia Delgado, a spokesman for the public transportation group.

Hundreds of anti-crime initiatives, from the hiring of former New York mayor Rudolph Giuliani as a consultant to the formation of elite commando groups to counter kidnappers, have been tried in recent years. Sunday, organizers handed out leaflets demanding a special session of Congress devoted to reforming public security laws and revamping the prison system.

"We can't bear it any longer," said Maria Eugenia Juarez, a marcher who said a member of her family had been kidnapped. "Something has to change."

Protesters jammed the Independence monument to voice concerns about crime.