America's nuclear forces apologise for tweeting joke about dropping something 'much bigger'

America's military body in charge of its nuclear weapons has apologised for a New Year's tweet joking it was always ready to "drop" a bomb when needed.

US Strategic Command, which is responsible for American cyber capabilities, missile defence and nuclear capabilities, tweeted that the tradition in New York was to drop the "big ball" in Times Square during the New Year countdown.

"If ever needed, we are ready to drop something much, much bigger," it said.

"Watch to the end!" it added, along with a video of B-2 Spirit Stealth Bombers dropping some very large conventional bombs and the flashing words “STEALTH,” “READY,” and “LETHAL”. 

The video concludes with two bombs released from a plane, followed by several massive explosions.

The post was soon deleted before the agency tweeted: "Our previous NYE tweet was in poor taste & does not reflect our values. We apologise. We are dedicated to the security of America & allies."

A spokesman said the video showed test footage of non-nuclear bombs.

"This post, which has since been deleted, was part of our Year in Review series meant to feature our command priorities: strategic deterrence, decisive response and combat-ready force," a spokesman told NBC News.

"It was a repost from earlier in the year, dropping a pair of conventional Massive Ordnance Penetrators (MOP) at a test range in the United States."

It is not the first time this year an arm of the US military has had to apologise for a tweet.

During a social media frenzy about the "yanny" and "laurel" audio clip, the US Air Force tweeted that the Taliban would have preferred to hear either word over gunfire. They later apologised and deleted the tweet.