A retired US admiral has warned governments to pay more attention to unidentified subs as they pose the "real threat" to international maritime security.

Rear Admiral and oceanographer Tim Gallaudet said Unidentified Submersible Objects - or USOs - need urgent and focused research as they could be lurking in the unexplored depths of our oceans.

In his latest report, Rear Admiral Gallaudet explained how this is an under-researched phenomenon, and not aliens hiding under our oceans.

The ex-US military described USOs as "large lighted craft", often seen under the sea surface on their own "or as part of a group in formation."

In a chilling warning, Gallaudet said these unknown bodies can sometimes travel in the deep ocean waters without ever emerging.

And because most research focuses on what is going on up in the sky, it means that major powers could be making moves underwater without barely anyone knowing.

Gallaudet said: "We have less research on transmedium UAP and USOs than is ideal.

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