Five Houston police officers were wounded in a shooting Monday while serving a search warrant for narcotics.

Suspects opened fire as soon as officers breached the door at a residence in southeast Houston, Police Chief Art Acevedo said at an evening press conference. Two suspects died at the scene from police gunfire, but Acevedo said police do not know how many suspects shot at police.

About a dozen narcotics officers and six patrol officers, Acevedo said, were at the scene to serve the warrant and provide support to investigate the sale of black tar heroin. Officers breached the front door just before 5 p.m. local time while announcing themselves and hitting the siren and lights on a patrol car.

Four officers were struck by semi-automatic pistol fire and another officer was injured in the knee but not by gunfire, officials said. Two officers were in critical but stable condition and undergoing surgery Monday night, Acevedo said. One officer with a shoulder wound was released late Monday, the department tweeted. The two other officers are expected to fully recover, but remained in the hospital on Monday night.

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Initially, Joe Gamaldi, president of the Houston Police Officers’ Union, tweeted that five officers had been shot.

"We are sick and tired of having targets on our backs," Gamaldi said at the police press conference. "We are sick and tired of dirtbags trying to take our lives when all we're trying to do is protect this community and protect our families."

First responders transported two officers by helicopter and three by ambulance, Houston Fire Chief Samuel Pena said. The injured officers ranged in age from 33 to 54.

In a statement, Texas Gov. Greg Abbott asked for prayers for the injured officers.

“This evening’s horrific attack on police officers is a solemn reminder of the service and sacrifice our brave men and women in law enforcement make every day to keep us safe. The city of Houston and the Houston Police Department will have whatever state resources they need to bring swift justice to those involved. I ask all Texans to join Cecilia and me in praying for the officers injured, and for the continued safety of all law enforcement officers who protect our communities.”

Contributing: The Associated Press