Some 20,000 people staged a protest in Mexico City on Sunday to call for an end to the drug violence engulfing the country.

The silent march started in cities across the country, and some protesters walked all the way to the nation’s capital and gathered in the central square, the BBC reports.

Leftist revolutionary group the Zapatista Army of National Liberation (Ejercito Zapatista de Liberacion Nacional – EZLN) announced that it was backing the protests. The group reportedly released a statement condemning the “psychotic military campaign by [President] Felipe Calderon,” and said it would hold its own protests in Chiapas, southern Mexico, on May 7.

The marches were led by Javier Sicilia, a well-known poet whose son was murdered, seemingly by a drug gang, along with some friends.

President Felipe Calderon is under pressure to take action to end the violence in Mexico, which many say has been increased by his hardline policies against drug gangs.