Expressing what has become regularly repeated frustration on the issue, US President Barack Obama said on Saturday that the United States needs to "do something" to make it harder for criminals and psychologically people to get guns after a shooting in Colorado killed three people and injured nine.

"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," Obama said. "Enough is enough."

In Friday's shooting, an assailant opened fire at a Planned Parenthood clinic, a center that provides health services including abortions.