The Pentagon has been running a secret multi-million dollar programme to investigate Unidentified Flying Objects, according to US reports.

Only a small number of officials were aware of the programme, which began in 2007 and was reportedly closed in 2012. Although its funding ceased, officials have reportedly continued to investigate sightings of unusual aerial phenomena and suspicious objects alongside their daily duties.

The New York Times says documents from the operation describe strange speeding aircraft and hovering objects.

But scientists were doubtful, stressing that unexplained happenings were not necessarily proof of alien life.

The brainchild of the Advanced Aerospace Threat Identification Programme was Harry Reid, a retired Democratic senator who was the Senate majority leader at the time.