Mexico's Senate has passed a bill authorizing police to use undercover agents against drug cartels and organized crime.

Many Mexican detectives currently operate in plain clothes, without uniforms. But the new measure would allow them to keep their identities secret in legal proceedings and be identified only by a numerical code known only to superiors.

Mexico's violent drug cartels have increasingly targeted police officials for assassination in recent years.

Criminal justice expert Jorge Chabat says the reform "is fundamental in order to fight drug trafficking." Chabat said Friday that allowing agents' names to be released "is like sending them into war without a rifle." The bill was approved Thursday, and now goes to the lower house.