A high-ranking Kiwi diplomat in the United States has drawn a warning from New Zealand's foreign affairs department after tweeting "we will all die" if the Democratic Party doesn't get its "s*** together".

The Ministry of Foreign Affairs and Trade says it's taking "appropriate action" after reports by website Newsroom that New Zealand's deputy head of mission to the United States, Caroline Beresford, had tweeted about US domestic elections.

On Saturday, Beresford tweeted the Democrats - the opposition to the current Trump administration - needed to "get your s*** together or we will all die".

The message and another - since deleted - came in reply to an article praising potential left-wing candidates for the US 2020 presidential election.

"The ministry does not in any way endorse the content or tone of the tweets, which we note were deleted," an MFAT spokeswoman said on Wednesday.

"Our code of conduct and guidelines around the use of social media set very clear expectations of staff when making public comment, including maintaining political neutrality and care in expressing personal opinion.

"These expectations were not met in this instance."

In a brief statement, Foreign Affairs Minister Winston Peters said he was aware of the complaint and confident the ministry was handling the response appropriately.

- NZ Newswire