KANSAS CITY, Mo. — A suburban St. Louis police officer was "ambushed" during a traffic stop Friday, injured critically after he was shot at least once from behind as he walked to his patrol car, authorities said.

The suspect — a man in his 30s who was paroled in early 2015 after serving time on a weapons charge — likely will be charged in the shooting, St. Louis County Police Chief Jon Belmar said at a news conference. Authorities have not provided the race or identity of the suspect or officer, who was described as a 9-year law enforcement veteran.

The shooting followed the previous night's attack in Dallas that killed five officers and wounded seven during a protest over the deaths of black men killed by police this week in Louisiana and Minnesota. But Ballwin Police Chief Kevin Scott said he "can't even begin to speculate" about a motive.

The officer was walking to his car after the initial conversation with the motorist he stopped for speeding when that driver "advanced quickly" on him from behind, firing at least three shots, Scott said. The officer "had no chance at all" to pull his handgun and "was completely helpless," Scott said, noting the encounter was recorded by the police car's dashcam.

"Make no mistake: We believe during this investigation that Ballwin officer was ambushed, period," Belmar said.

After the shooting, Belmar said, the suspect sped away before an officer from another police department spotted the car about four miles away. The suspect abandoned his vehicle and fled on foot before being arrested about five minutes later, Belmar said.

The suspect was on probation for a weapons violation in St. Louis, Belmar said, had been on probation for a stolen vehicle in Oklahoma and was picked up for a gun violation in California, drawing a prison term for being a felon in possession of a firearm. He was paroled in March 2015.

Citing his concern about the shooting and the Dallas tragedy, Missouri Gov. Jay Nixon opted against leaving Friday for an eight-day overseas trade mission as planned and instead would return to Missouri from a Philadelphia event, spokeswoman Channing Grate said.

The shootings of officers in Ballwin, Dallas, Tennessee and Georgia in a 24-hour period prompted police agencies regionally and elsewhere in the U.S. to take precautionary safety measures. Earlier Friday, St. Louis Police Chief Sam Dotson said his city's law officers will work in pairs until further notice because of the Dallas killings, and that all officers must wear bullet-resistant vests when on duty outside of police stations.

Dotson said his department has gone to 12-hour days now through the weekend, given the national debate about policing and minorities.

"It's an unfortunate state of events we're dealing with right now," Belmar said. "I do understand the silent majority out there supports us."

Associated Press reporters Maria Fisher and Bill Draper in Kansas City, Summer Ballentine in Jefferson City, Missouri, and AP researcher Jennifer Farrar in New York contributed to this report.