Violence has spiked since President Felipe Calderon, who took office at the end of 2006, launched a crackdown on drug trafficking and related attacks, including the deployment of more than 36,000 soldiers across the country.

A swarm dressed in white, many carrying white flowers, set off from the capital's Independence Angel monument in the largest march, walking in silence towards the main Zocalo square, which has a capacity for 160,000 people.

Similar protests began earlier across the country, in all of Mexico's 32 states, many starting in unison.

Organisers hoped to bring hundreds of thousands to the streets, as in 2004 when almost half a million protested against kidnappings and insecurity, forcing the Government to carry out purges of the notoriously corrupt police and other reforms.

The Reforma daily newspaper said the past week had been the most violent since Mr Calderon launched his offensive, with 167 murders, including 24 police officers killed and 21 decapitated bodies found, including the discovery of the heads of two sisters in northern Durango state on Saturday.

''That's enough now. No more impunity,'' one banner in Mexico City read. Another read, ''Magistrates, no more revoking sentences''.

About 2700 people have died so far this year in gangland-style killings more than in all of 2007 across the country, according to national media, and Mexico has overtaken Colombia and Iraq with its kidnapping record.

Children dressed in white and carrying white balloons led an earlier march, gathering more than 3000 people in the central city of Pachuca, capital of Hidalgo state.

The recent high-profile kidnapping and assassination of 14-year-old Fernando Marti on his way to school in Mexico City a crime in which police were involved unleashed the latest wave of public anger over insecurity and systemic corruption.

The march organisers plan to hand a document containing citizens' requests to Mr Calderon and Mayor Marcelo Ebrard today. AFP