At least four people were killed when a gunman opened fire at a hospital in Chicago on Monday afternoon. The dead include a police officer, a doctor and a pharmaceutical assistant, as well as the shooter himself, NBC Chicago reported.

Police Superintendent Eddie Johnson said the shooter was in a relationship with the doctor, and had an argument with her at Mercy Hospital’s parking lot at around 3.28 pm local time (2.58 am India Standard Time). When another person tried to intervene, the shooter took out his handgun. He then shot the doctor, Johnson said.

Various media reports said it was unclear if the shooter was killed by the police or took his own life.

The gunman also fired at police officers who arrived on the scene. During the exchange of fire, a pharmaceutical assistant exiting an elevator was killed. Police officer Samuel Jimenez was also shot fatally, NBC Chicago said.

The shooter is yet to be identified, Time reported. Mercy Hospital said around 4.40 pm local time (4.08 am IST) that the incident was under control and that the police “have secured the hospital and patients are safe”.

On October 28, a gunman had killed 11 people and wounded six at a synagogue in Pittsburgh, Pennsylvania. The assailant stormed the Tree of Life synagogue in the Squirrel Hill neighbourhood in Pittsburgh, shouting “All Jews must die” as he fired his weapon.