She had asked Mr Trump to clarify a statement he made on Twitter the previous day. In that statement he had said the US "must greatly strengthen and expand its nuclear capability until such time as the world comes to its senses regarding nukes".

Mr Trump's spokesman Sean Spicer later said the president-elect's intention was to put other countries on notice not to expand their nuclear capabilities.

Mr Spicer said: "It's a warning to them that this president isn't going to sit idly by. He's a man of action. He's not going to sit back and allow that to happen without acting in kind.

"He will not take anything off the table. He is going to do what it takes to protect our country. And what's going to happen is they will come to their senses and we will all be just fine."

At the same time Mr Trump was declaring an arms race Mr Putin was holding his end of year press conference in Moscow.

In it Mr Putin said he was unconcerned about the prospect of a US nuclear build-up, and called Mr Trump's tweet "nothing surprising".