US Navy officials have been left red-faced after one of their jet pilots drew a large penis in the sky over Washington state.

Images posted on social media showed the image stretching high over Okanogan County.

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"The actions of this aircrew are wholly unacceptable and antithetical to Navy core values," said a statement issued by the NAS Whidbey Island airbase.

"We have grounded the aircrew and are conducting a thorough investigation, and we will hold those responsible accountable for their actions.

"The Navy apologises for this irresponsible and immature act, and anyone who was offended by this unacceptable action."

The aircraft involved was an E/A-18 Growler, the Navy said.

The carrier-based plane carries a two-person crew.

The plane flew over the small town in a pattern "that left a condensed air trail resembling an obscene image to observers on the ground", the Navy said.

"Sophomoric and immature antics of a sexual nature have no place in Naval aviation today," Vice Admiral Mike Shoemaker, the commander of Naval Air Forces, added in a statement.

"We will investigate this incident to get all the facts and act accordingly."

The names of the air crew were not released.

A local television station said one mother in Okanogan County was concerned she might have to explain the image to her young children.

But local resident Ramone Duran told the Seattle Times newspaper that "after it made the circles at the bottom, I knew what it was and started laughing".

This is not the first time an air crew has pulled such a stunt, the BBC reported.

In August an RAF fighter pilot drew a 56-kilometre penis on radar monitoring the skies over Lincolnshire, England.

Reuters/AP