FERGUSON (Missouri): The shooting of two police officers during a protest rally in Ferguson, Missouri, sparked a sweeping manhunt for suspects on Thursday and ratcheted up tensions in a city at the centre of a national debate over race and policing.

US President Barack Obama and Attorney General Eric Holder condemned the attack on the officers, who were treated for wounds at a local hospital and released.

“What happened last night was a pure ambush,” Holder said at a press conference. “This was not someone who was trying to bring healing to Ferguson; this was a damn punk.” 

The two officers were part of a security detail at a rally being staged in front of the Ferguson police station when they were hit by gunfire.

Demonstrators had gathered to demand sweeping changes in the St. Louis suburb after the release of a scathing US Justice Department report that found that deep-rooted racial bias within its mostly white police force. The report grew out of the shooting in August of an unarmed black teenager by a white police officer.

While condemning the wounding of the officers, organizers vowed more protests on Thursday night.

“We deplore all forms of violence,” said Reverend Osagyefo Sekou, who was in the crowd when shots rang out. “But we also deplore the findings of the Department of Justice report and the suffering and the misery that this community has endured.” 

To prevent further violence, St. Louis County police and the state’s Highway Patrol will take over security from the mostly white Ferguson force during any demonstrations.

The state took a similar step in November after two nights of rioting that followed the announcement that a grand jury would recommend no charges in the killing of 18-year-old Michael Brown. Outrage over the officer’s use of deadly force and how the justice system handled it touched off a nationwide wave of protests.

Thursday’s shooting left a 41-year-old St. Louis County police officer with a shoulder wound and a 32-year-old officer from nearby Webster Groves Police Department with a bullet lodged near his ear, St. Louis County Police Chief Jon Belmar said.

Two Missouri congressman offered a $3,000 reward for information leading to an arrest.

In one video taken at the chaotic scene after the gunfire, a witness can be heard commenting, “Acknowledgement nine months ago would have kept that from happening.” 

The shooting came less than three months after a man ambushed two New York City patrolmen, seeking to avenge the killings of Brown and an unarmed black man in New York.

The White House sent a Tweet that read: “Violence against police is unacceptable,” a message echoed by Brown’s family. “We reject any kind of violence directed toward members of law enforcement,” they said in a statement.

Investigators wasted no time in bringing people in for questioning but all of them were later released and no arrests were made, the St. Louis County Police said.

The shooter used a handgun and shell casings had been recovered, Belmar said.

Police and protesters appeared to disagree about where the shots originated. Belmar, who said police did not return fire, asserted the gunshots came from the middle of the crowd.

“I don’t know who did the shooting … but somehow they were embedded in that group of folks,” Belmar said.

Protesters at the scene insisted the shots came from further away. “The shooter was not with the protesters. The shooter was atop the hill,” activist DeRay McKesson said on Twitter.

Tom Jackson, the police chief, was the latest in a string of Ferguson officials who have quit after the Justice Department report. It found that the city used police to issue traffic citations to black residents to boost its coffers. The harassment created a “toxic environment.” 

The shooting reignited a months-long debate over the use of force by police against minority groups. Among the trending Twitter hashtags was #BlueLivesMatter, a reference to the blue uniforms often worn by US police and a play on the #BlackLivesMatter slogan popularized by Ferguson protesters.

“A police officer can get away with killing someone on video. Black ppl are often blamed for crimes they didn’t commit. But #BlueLivesMatter,” read a Tweet from Keziyah Lewis.