Washington (AFP) - Republican US Senator Rand Paul called for the demilitarization of the police Thursday, blaming "big government" for the clashes which flared following the killing of an unarmed black teenager .

Paul, seen as a contender for the Republican 2016 presidential election ticket, argued in a commentary on Time magazine's website that the crisis reflected a "systemic problem" of US law enforcement, which is often tainted by racism.

"Anyone who thinks that race does not skew the application of criminal justice in this country is just not paying close enough attention," said the Kentucky senator. "And the root of the problem is big government."

Paul the trend towards police forces equipping themselves with military style equipment, suggesting it had played a part in the violence in Ferguson, a suburb of the midwestern city of St Louis, where officers with assault rifles faced unarmed protesters.

"If I had been told to get out of the street as a teenager, there would have been a distinct possibility that I might have smarted off. But, I wouldn't have expected to be shot," he said.

"There is a legitimate role for the police to keep the peace, but there should be a difference between a police response and a military response. The images and scenes we continue to see in Ferguson resemble war more than traditional police action."

Paul said the federal government had "incentivized the militarization of local police precincts" by helping local government "build what are essentially small armies."

"That goes far beyond what most of Americans think of as law enforcement," Paul said.

"When you couple this militarization of law enforcement with an erosion of civil liberties and due process that allows the police to become judge and jury ... we begin to have a very serious problem on our hands."