Image copyright AP Image caption The Air Force said the security of the US nuclear programme had not been threatened

The number of US airmen embroiled in a nuclear cheating scandal has doubled to several dozen, officials speaking on condition of anonymity say.

Thirty-four US Air Force officers in charge of launching nuclear missiles were suspended earlier this month.

They are accused of cheating in monthly proficiency tests.

The US Air Force said some staff had texted answers to the routine tests to others, while others had known about the cheating but failed to report it.

The ranks included captains.

The allegations emerged during investigations into alleged drug use by personnel at other bases.

It was not immediately clear whether the additional 30 or so airmen implicated were alleged to have participated in the cheating or were involved in an indirect way.

An Air Force spokeswoman said earlier this month that the entire team at Malmstrom Air Force Base in Montana in charge of overseeing missile launches would be re-tested.

Defence Secretary Chuck Hagel ordered a high-level review of the US nuclear forces last week, saying he was "deeply concerned" about morale and discipline among nuclear officers - but insisted that US nuclear arms were safe.