File photo taken on July 21, 2016 shows Donald Trump taking the stage on the last day of the Republican National Convention in Cleveland, Ohio, the United States. (Xinhua/Yin Bogu)

WASHINGTON, Dec. 22 (Xinhua) -- U.S. President-elect Donald Trump on Thursday called for the United States to "strengthen and expand" its nuclear capabilities.

"The United States must greatly strengthen and expand its nuclear capability until such time as the world comes to its senses regarding nukes," the President-elect tweeted.

The United States is expected to spend one trillion dollars over the next 30 years upgrading its nuclear arsenal, according to a TheHill news daily report.

However, it's not immediately clear what prompted Trump's new proposal and what are the details behind.

On the presidential campaign trail, Trump, counter to the past and current U.S. stance, proposed that countries such as Saudi Arabia and Japan should acquire nuclear weapons, stirring sharp criticism at home and abroad at the time.