LOS ANGELES (AFP) - Police on Saturday (Nov 28) were questioning a man arrested for allegedly killing three people and wounding nine others when he entered a family planning centre in Colorado with a rifle and opened fire.

An usually busy area of snow-covered Colorado Springs was placed on lockdown on Friday (Nov 27) afternoon, one day after Americans celebrated the Thanksgiving holiday, in the latest incident to shine a spotlight on gun violence in the United States.

"Enough is enough," said US President Barack Obama, as he revealed that the shooter used a military-style assault rifle.

"We have to do something about the easy accessibility of weapons of war on our streets to people who have no business wielding them. Period. Enough is enough," Obama said in a statement.

He also disclosed for the first time that the arrested man had held hostages at the family planning centre from which he opened fire at people outside in an hours long standoff with police.

Obama said it was particularly sad that one day after a holiday - Thanksgiving - Americans have to comfort families who suddenly lost loved ones to gun violence.

"And yet, two days after Thanksgiving, that's what we are forced to do again," Obama said.

The gunman entered a Planned Parenthood clinic around noon local time on Friday armed with what police described as a "long weapon" and opened fire from a window. Police surrounded the building, and after an exchange of gunfire and a stand-off lasting more than five hours, the gunman surrendered at around 5pm local time.

Officials identified the suspect as 57-year-old Robert Lewis Dear of South Carolina, US media reported.

Several news reports, including CNN, said that Dear appeared to be armed with an AK-47-type rifle.

There is no known motive for the shootings, and it was unclear whether Planned Parenthood - a major women's health and family planning group - was the shooter's target.

Abortion is one of many services Planned Parenthood provides for women, and the association has become a lightning rod for criticism by social conservatives.

Colorado Springs Mayor John Suthers paid tribute to police for hauling in the gunman without further bloodshed.

A police officer was among the dead, he said, while nine others - among them five police officers - were wounded, though none seriously.

"While this was a terrible, terrible tragedy, it could have been much worse if not for the reactions of first responders," Mr Sutter told reporters.

The dead policeman was identified as Mr Garrett Swasey, 44, a campus officer at the University of Colorado at Colorado Springs who had raced to the scene of the shooting.

Officers were able to enter the building during the stand-off and convince Dear to surrender, police spokesman Catherine Buckley told reporters.

Ms Vicki Cowart, president and chief executive of Planned Parenthood Rocky Mountains, said she did not believe the centre had been specifically targeted.

"We're very pleased that our own security systems were operating at top-notch," she added.

That included people scrambling into a "safe room" for cover.

"Some got out early throughout the afternoon, but those that didn't were in a safe spot," Ms Cowart told CNN.

Critics, many of whom seek to outlaw abortion in the United States, have falsely accused Planned Parenthood of selling fetal organs and body parts for profit, and encouraging women to have abortions in order to expand such operations.

The national Planned Parenthood office praised "the brave law enforcement officers who put themselves in harm's way" in the incident.

"We are profoundly grateful for their heroism in helping to protect all women, men and young people as they access basic health care in this country," the statement read.

Local media said that extra police were sent to protect the three other Planned Parenthood clinics in the Denver area.

Police initially feared that Dear might have brought explosives, and officers carefully combed the crime scene overnight after the gunman surrendered.

Several people were inside the clinic at the time of the shooting on what had been a regular work day.

When the gunman opened fire, terrified people fled the building and into the snow, some crying and pleading for help.

The immediate area around the clinic was placed on lockdown and people were told to stay indoors.

A sheriff's department Swat team with at least one armoured vehicle rushed to the scene.

Lt Buckley said the shooter was armed with some kind of "long weapon" with a shoulder stock such as a rifle, and some witnesses reported hearing automatic fire.

Mr Quan Hoang, the owner of a nearby nail salon, told CNN that when he heard the gunfire, he feared a robbery was under way at a bank in the shopping area, which would have been bustling with people looking for Black Friday sales bargains the day after Thanksgiving.

"And we see cops, Swat, the bomb squad, a whole bunch of people just trying to take cover around the Planned Parenthood area," he said by telephone.

"An officer came back in and said, 'Is everyone safe?' We asked him questions and he said they've barricaded him inside the Planned Parenthood and he was shooting out from the windows."