Image copyright AP Image caption The security forces patrol the missile fields and respond to emergencies

The US Air Force is investigating 14 guards at a nuclear weapons site after they were accused of using illegal drugs, including cocaine.

The Air Force announced the probe at FE Warren Air Force Base in the US state of Wyoming on Friday.

The defence corps has been scrutinised for insufficient training and poor personal conduct in recent years.

Its command guards the fleet of Minuteman 3 land-based nuclear missiles.

The 14 are accused of "credible" off-duty drug "activity", General Robin Rand told the AP news agency.

"This is very important to me that we get to the bottom of this," he said, and that he believes most airmen do adhere to Air Force rules.

The accused airmen, who have been removed from duty, are not the ones who actually control the missiles at the 1,300-airmen base.

Security forces at the base patrol missile fields and respond to emergencies.

Past misconduct

Two years ago, some missileers - the officers who launch the missiles - were under investigation for drug use. That investigation found that several dozen of the missileers had cheated on their proficiency tests at another air base.

Some staff had texted answers to the routine tests to others, while others had known about the cheating but failed to report it.

Nine mid-level nuclear commanders were later fired.

"Personnel failures within this force threaten to jeopardize the trust the American people have placed in us to keep our nuclear weapons safe and secure," then-Defence Secretary Chuck Hagel said.