Gunmen shot two police officers in a Monterrey suburb whose police chief was slain two months ago, authorities said Thursday.

At least two assailants opened fire on officers Ramiro Calvillo, 33, and Martha Guillen, 32, in the drive-by shooting Wednesday night in the Monterrey suburb of Santa Catarina. The officers died shortly after arriving at a hospital, authorities said.

Calvillo and Guillen had finished their shift and were helping a driver whose car had broken down when they were attacked, said Alberto Flores, director of public safety in Santa Catarina.

Authorities were investigating and had made no arrests.

In November, a lone gunman killed Santa Catarina Police Chief Baltazar Gomez inside a convenience store three weeks after he had assumed the post.

The border has seen a wave of violence attributed to a battle between the Sinaloa and Gulf drug cartels for billion-dollar smuggling routes into the United States. The struggle has spawned beheadings, grenade attacks and execution-style killings of rival gangsters and police officers.

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