Authorities were searching on Sunday for two men suspected of shooting and wounding a police officer in Ferguson, the St Louis suburb where there have been angry protests since a white officer fatally shot an unarmed 18-year-old black man, Michael Brown, last month.

Although there were two separate protests about the 9 August shooting of Brown happening around the time the officer was shot on Saturday night, St Louis County police chief Jon Belmar said he didn’t think they were related in any way to the attack on the officer.

The men fled when the officer approached them at around 9pm because the community center they were standing outside of was closed, Belmar said at a news conference early on Sunday. When the officer gave chase, one of the men turned and shot him in the arm, he said.

Belmar said the officer is expected to survive, but he didn’t identify the officer or give further details about his condition. He said the officer returned fire, but that police have no indication that either suspect was shot.

The shooting comes amid simmering tension between many community members and the police in Ferguson, where two-thirds of residents are black, but only three of the city’s 53 officers are African-American.

At around midnight on Saturday, about two dozen officers stood near a group of about 100 protesters who mingled on a street corner, occasionally shouting, “No justice, no peace.” Meanwhile, police had closed part of a nearby street as helicopters and officers from several law enforcement agencies searched the area for the two suspects.

Earlier on Saturday, Brown’s parents told the Associated Press they were unmoved by a videotaped apology released days earlier by Ferguson police chief Tom Jackson, whose attempt to march with protesters on Thursday sparked a clash that led to several arrests.

When asked if Jackson should be fired, Brown’s mother, Lesley McSpadden, said he should be. Brown’s father, Michael Brown Sr, said rather than an apology, they would like Darren Wilson, the officer who shot their son, to be arrested. A county grand jury is weighing whether to indict Wilson in Brown’s shooting.

The Justice Department, which is investigating whether Brown’s civil rights were violated, is conducting a broader probe into the Ferguson police department. On Friday, it urged Jackson to ban his officers from wearing bracelets supporting Wilson while on duty and from covering up their name plates with black tape.

Ferguson residents complained about the bracelets, which are black with “I am Darren Wilson” in white lettering, at a meeting with federal officials this week.

Also early on Sunday, not far from Ferguson, an off-duty St Louis city police officer was injured on Interstate 70 when three suspects fired shots into his personal vehicle, a police spokeswoman said.

Schron Jackson said the officer, who has nearly 20 years of experience, was being treated at a hospital for a minor injury to his arm from broken glass. She said there was no reason to believe the two shootings were related.

Missouri Governor Jay Nixon expressed sympathy for the injured officers in a conference call on Sunday from Afghanistan with reporters from Missouri. He described the violence as “a challenge for everyone”.