Caroline Beresford, Wellington’s second-ranked diplomat in the US, sent at least three tweets late last week disagreeing with an opinion column on political news website “The Hill”.
She rebuffed a claim that a 2020 Democratic ticket with Mr Sanders and Ms Warren could “win big”.
She tweeted: “No it couldn’t. Please get your shit together or we will all die.
Later adding: “They’ve learned nothing.”
Ms Beresford deleted her controversial tweets after she faced widespread backlash.
But they came as Mr Sanders and Ms Warren are being urged to run against Mr Trump’s right-wing populism in the next presidential race.
New Zealand’s Ministry of Foreign Affairs and Trade (MFAT) told stuff.co.nz the department “does not in any way endorse the content or tone of the tweets”.
The MFAT also vowed to enact “appropriate action”.
A spokesman said: “The ministry does not in any way endorse the content or tone of the tweets.”
Ms Beresford told news website Newsroom, which first reported the story, that she’d personally sent the tweets, but “realised very quickly that they were inappropriate, which is why I deleted them”.
Ms Beresford is in charge of New Zealand’s day-to-day diplomatic mission in the United States, and is ranked below only Ambassador Tim Groser.
New Zealand considers the US a close ally, and the two nations are part of the “Five Eyes” intelligence gathering network, which also includes Australia, Canada and the UK.
The US Embassy in New Zealand said it worked closely with its “hardworking, professional New Zealand counterparts” and held them in the highest regard.