For the third time in a just over a week, Boston police fired at armed suspects in Dorchester, officials said.

Anthony Toombs, 21, of Dorchester, is expected to be arraigned today in Dorchester District Court on charges of unlawful possession of a firearm, unlawful possession of ammunition, unlawful discharging of a firearm within 500 feet of a building, assault with a dangerous weapon, assault and battery on a public employee, resisting arrest, and carrying a loaded firearm, Suffolk district attorney’s office spokesman Jake Wark said.

At around 1 a.m. today, police were investigating a drug transaction on Blue Hill Avenue. Toombs, who was allegedly involved in the transaction, allegedly shot at one of the officers, who then fired back, according to a statement from the district attorney’s office.

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No one was hit during the shootout. Toombs allegedly struck an officer while he was being taken into custody. The officer sustained minor injuries, the statement said.

In an earlier incident at 12:48 a.m. on Tuesday, police chased a man who shot at a moving vehicle in near Kingsdale and Wales streets. During the chase officers ordered the suspect, Michael Coke, 38, of Roxbury to drop his weapon and fired when he did not comply. No one was injured, according to a statement from the Suffolk district attorney’s office.

Coke, who has a history of gun offenses, was ordered held on $200,000 bail on charges of assault with a dangerous weapon, unlawful possession of a firearm as a subsequent offense, unlawful possession of ammunition, and discharging a firearm within 500 feet of a dwelling, according to the statement.

On Aug. 7 at around 2 p.m., two officers were working on an undercover drug investigation on Dorchester Avenue. The officers identified themselves to two suspicious men, and one raised his weapon and shot at the officers, police said.

Police killed one of the men, Roudy Hendricks, 20, of Brockton. The other suspect was arrested for violating his probation a few days later, police said.

Both officers, Harry Jean and Terry Cotton, sustained injuries to their leg during the incident, police said.