WASHINGTON (AP) — A spokesman says the president-elect is putting other countries on notice with his tweet calling for greatly expanded U.S. nuclear capability.

The spokesman says Donald Trump was responding to Russia, China and other countries talking about expanding their own nuclear capabilities.

Sean Spicer said Friday, “The president isn’t saying we’re going to do this. He said, ‘unless they come to their senses.’ It’s a warning to them that this president isn’t going to sit idly by.”

Also Friday, MSNBC reported that Trump said: “Let it be an arms race, because we will outmatch them at every pass and outlast them all.”

The network’s “Morning Joe” host Mika Brzezinski said Trump made the statement in a phone call with her.

Spicer spoke on Fox News and NBC’s “Today.”

The United States must greatly strengthen and expand its nuclear capability until such time as the world comes to its senses regarding nukes

— Donald J. Trump (@realDonaldTrump) December 22, 2016