(Andrew Harnik/AP)

President Obama on Saturday called for additional gun control measures in the United States, after the slaying of three people Friday at a Planned Parenthood clinic in Colorado.

In a written statement, Obama said that regardless of the motive, it was unacceptable that these sort of mass shootings happen so frequently in the United States.

"This is not normal. We can’t let it become normal," he said. "If we truly care about this — if we’re going to offer up our thoughts and prayers again, for God knows how many times, with a truly clean conscience — then 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."

Administration officials have been scrutinizing whether they can undertake additional gun controls through executive action, but no proposals have yet to be finalized. The leading proposal would impose new background-check requirements for buyers who purchase weapons from high-volume gun dealers.

[This is what President Obama plans to do on gun control]

Two weeks ago, Obama told HBO's Bill Simmons that any forthcoming proposals are still undergoing legal review. "There are maybe a few more that had to be scrubbed by lawyers because essentially, with every executive action, we can count on it being challenged by somebody in Congress or, in this case, the NRA. We want to make any executive action we take as defensible as possible legally."

In Saturday's statement, Obama said, "We don’t yet know what this particular gunman’s so-called motive was for shooting twelve people, or for terrorizing an entire community, when he opened fire with an assault weapon and took hostages at a Planned Parenthood center in Colorado."

"What we do know is that he killed a cop in the line of duty, along with two of the citizens that police officer was trying to protect. We know that law enforcement saved lives, as so many of them do every day, all across America," he said. "And we know that more Americans and their families had fear forced upon them."

"May God bless Officer Garrett Swasey and the Americans he tried to save -- and may He grant the rest of us the courage to do the same thing," the president added.