Police officers secure a road near the Planned Parenthood center in Colorado Springs, Nov. 27

COLORADO SPRINGS, Colo. — Police on Friday swarmed an area around a Planned Parenthood abortion clinic in Colorado Springs, where a gunman opened fire, injuring three officers and an undetermined number of civilians, police and hospital officials said.

City police said in a Twitter message about two hours after the shooting was first reported that the situation remained unstable, contrary to an ABC News report, attributed to a police commander, that the suspect was thought to have been “contained.”

“This is an active situation,” a police department spokeswoman, Lieutenant Catherine Buckley, told CNN, adding that law enforcement had yet to confirm the gunman’s location.

She said police also were not sure that shooting had any connection to Planned Parenthood and that circumstances surrounding the gunfire remained unclear.

CBS News reported that a gunman fired shots upon entering the clinic, which was guarded by security, and that law enforcement officials were concerned about the possibility explosives being involved.

At least three officers and an unknown number of civilians were injured in the shooting, the Colorado Springs Police Department said on Twitter.

A spokeswoman for Penrose-St. Francis Medical Center in Colorado Springs confirmed the hospital received three patients from the shooting but the nature and extent of their injuries were not immediately provided.

At the outset of the situation, police said in a Twitter post that a call for assistance referred to a person firing a gun in the city’s northwest side, on Centennial Boulevard, where the Planned Parenthood center is located.

The facility provides abortions, screening for sexually transmitted diseases, pregnancy testing and other services, according to its website.

The clinic was open for business on Friday, according to Cathy Alderman, a spokeswoman for Planned Parenthood of the Rocky Mountains.

“At this time, our concern is for the safety of our patients, staff and law enforcement,” Vicki Cowart, president of Planned Parenthood Rocky Mountains, said in a statement.

As in much of the rest of the country, abortion is a divisive issue in the politically competitive state of Colorado, figuring prominently in attack ads during last year’s hard-fought Senate race between incumbent Democrat Mark Udall and Republican challenger Cory Gardner, the winner of the election.

The Colorado Springs clinic has been the target of repeated protests and in recent years moved to its current location, which has been derided as a “fortress” by abortion foes.

Hundreds of protesters picketed in front of the clinic in August as part of a push by abortion opponents to cut off public funding for Planned Parenthood, according to the Colorado Springs Gazette.

One man was charged with trespassing in 2012 after flouting as many as 30 warnings to keep of clinic property, the paper said

Early police reports painted a chaotic picture of the situation.

“The area is NOT secure. Media do not stage in the area,” the police department said in its tweet, urging members of the public in a nearby shopping center to “shelter in place.”

Brigette Wolfe, who works across the street from the scene, told CNN she could see law enforcement officers including police SWAT teams deployed in the area.

Colorado Springs, about 70 miles south of Denver, was the scene of a mass shooting on Oct. 31 in which a gunman killed three people near downtown before dying in a shootout with police.

The city is home to the U.S. Air Force Academy and the U.S. Olympic training center.