WASHINGTON (AFP) - US President Barack Obama said Friday it can be beneficial for high-profile athletes to speak out on social issues, after a string of sports stars have protested over police killings of black Americans.

"There are important issues out there and for athletes to recognise they're citizens as well as entertainers and they've got a voice that's legitimate, I think is important - I think it's useful," Obama said in an interview on ESPN radio.

The President noted that revered athletes such as boxing icon Muhammad Ali and tennis great Arthur Ashe used their stature to focus attention on social or political issues.

Recently, five players for the NFL's St Louis Rams entered their playing field with the "hands up, don't shoot" gesture adopted by protesters in Ferguson, Missouri, where a white policeman shot dead an unarmed black teenager.

Numerous players in both the NFL and NBA - including former NBA Most Valuable Players Derrick Rose and LeBron James - have donned T-shirts reading "I can't breathe," the last words spoken by African American father-of-six Eric Garner who died after he was held in a chokehold by a New York police officer.

Obama, on the radio show to promote a health-care sign-up, was critical of the NFL's handling of the Ray Rice domestic violence case, saying the league was "behind the curve" in its response.

"You don't want to be winging it when something like this happens," Obama said.

"You want to have clear policies in place. The fact that policies have now been established I think will be helpful in sending a message that there's no place for that kind of behavior in society, whether it's in sports or anyplace else," he said.

At least, the case raised awareness of the problem, Obama said.

"Obviously, the situation that happened in the Rice family was unfortunate, but it did lift up awareness that this is a real problem that we have to root out and men have to change their attitudes and their behaviour," he said.