President Trump reportedly told Russian President Vladimir Putin during a phone call the U.S. would beat Russia if the two nations were to engage in an arms race.

"If you want to have an arms race we can do that, but I'll win," Trump warned Putin, according to two White House officials who spoke to NBC News .

The president has faced intense scrutiny for congratulating the Russian president for winning his re-election bid during the phone call last week, but administration officials argue Trump has recently taken a harsher tone regarding Putin behind the scenes.

Sources told NBC News the shift in approach is a reactionary one since Putin began challenging the president’s strength and flaunting their new nuclear weapons system that could reach the U.S., a threat that reportedly “really got under the president’s skin.”

Following the phone call, the president dismissed any sign of tensions to reporters and claimed the two had future plans to discuss standing down from an arms race.