The shooting at the Planned Parenthood clinic in Colorado Springs has left two civilians and a police officer dead, with the suspected gunman under arrest.
Nine other people were injured during the standoff at the family planning clinic, which lasted five hours before the suspect surrendered.
A number of people were trapped inside the building as shots were exchanged.
The motive remains unclear. The Planned Parenthood group has drawn anti-abortion protests in the past.
A law enforcement source identified the suspect as Robert Lewis Dear, from North Carolina. No other details were given.
“Obviously, we lost two civilian victims. We mourn the loss of a very brave police officer.”
The dead police officer was named as Garrett Swasey, 44, who was married with two children.
Colorado Springs Police Chief Peter Carey said five police officers were among the injured, who were being treated in local hospitals.
Police had sealed off streets around the centre as officers tried to make contact with the suspect.
“We did get officers inside the building,” police Lt Catherine Buckley said.
“They were able to shout to the suspect and make communication with him and at that point they were able to get him to surrender and he was taken into custody.”
According to police, the suspect had been seen carrying “some bags” into the building and teams were combing the area for possible explosives.
Robert Lewis Dear’s car which was found nearby was also being checked for explosives, CNN reported.
The manager of a nearby hair salon said she had heard as many as 20 gunshots in less than five minutes.
Denise Speller told a local newspaper she had seen one of two police officers appear to fall to the ground and the other attempt to get the wounded officer behind their police vehicle.
Police had told shoppers at a nearby centre to stay indoors.
In a statement, the family planning clinic said it was not yet clear “if Planned Parenthood was in fact the target of this attack”.
“Our concern is for the safety of our patients, staff and law enforcement,” said its CEO, Vicki Cowart.
Planned Parenthood has been the focus of protests recently after an anti-abortion organization secretly recorded a Planned Parenthood official discussing how to obtain aborted fetal tissue for medical research.
Pro-life advocates say this proves Planned Parenthood is selling fetal parts for profit – which is illegal – but this is disputed by the organization.
New York’s city police said it had deployed critical response vehicles to Planned Parenthood sites in the city because of the Colorado incident, but said there was no threat in the city.