One officer and two gunmen were killed and eight other officers wounded Friday when a contingent of the Barrio 18 gang attacked police, Salvadoran authorities said.
The assault occurred as officers from a tactical unit were searching for illegal weapons in a poor neighborhood of San Salvador.
One of the gunmen killed was identified as a leader of Barrio 18 operations in the town of Panchimalco suspected of a role in more than a dozen murders.
The director of the capital's General Hospital, Evelyn Alvarenga, told reporters that the eight officers hurt in the clash arrived with "superficial" bullet wounds in their arms and legs.
Four of the officers have already been treated and released, while the other four are likely to leave the hospital within a week, she said.
El Salvador, with 60 homicides for every 100,000 inhabitants in 2017, is regarded as one of the world's most dangerous countries.