The United States' embassy in Canberra has apologised for a "training error" after distributing a fake meeting invitation, complete with a photo of a pyjama-wearing cat.

The email, titled "meeting", featured a photo of a tabby cat wearing a blue Cookie Monster outfit and holding a plate of choc-chip biscuits, beneath the title "cat pajama-jam".

In a clear case of misdirected correspondence last week, the email also contained a section of Latin and recipients were given the option to hit an RSVP tab.

It's unknown how widely the email, sent by the US Department of State, was distributed.

US Mission to Australia public affairs counsellor Gavin Sundwall kept his apology lighthearted.

"Sorry to disappoint those of you who were hoping to attend this 'cat pajama-jam' party, but such an event falls well outside our area of expertise," he wrote in a follow-up email two days after the original.

"It was a training error made by one of our new staff testing out our email newsletter platform."

Mr Sundwall said "strong new management controls" would be added to prevent a repeat of the mistake.