Local media said Francisco Ortiz Franco, of the weekly Zeta, was gunned down by masked men in Tijuana.

There have been several attacks on the paper's staff, including the murder of its founder 16 years ago.

The Mexican attorney general said if Mr Ortiz's death proved to be linked to organised crime, the federal authorities would take over the case.

Hit three times

Officials in the Mexican state of Baja California said Mr Ortiz had just left a clinic with his two children, when men in a pick-up truck opened fire.

He was hit by three bullets, they said. His children, aged eight and 10, were unharmed.

Mr Ortiz was one of three editors at the newspaper. He had trained as a lawyer and had a column specialising in legal affairs.

Zeta is renowned for reporting on the influence of drug traffickers in Tijuana, a city on the US border where several drug gangs are thought to be based.

A co-founder of the paper, Hector Felix Miranda, was ambushed and killed in 1988.

Running for mayor

One of those convicted of the murder was a bodyguard at a race track owned by businessman Jorge Hank Rhon, who comes from one of Mexico's most powerful political families and who is currently running to be mayor of the city.

Every week since Felix Miranda's death, Zeta has published a full-page notice under his name, asking: "Jorge Hank Rhon: why did your bodyguard Antonio Vera Palestina kill me?"

In 1997, the newspaper's publisher, Jesus Blancornelas, was badly wounded in a gangland attack.