US President-elect Donald Trump's pick for national security advisor says he expects a telephone call between Trump and Russian President Vladimir Putin to take place in coming weeks.

Mike Waltz, a member of the House of Representatives, appeared on an ABC television program on Sunday. Trump said earlier that a meeting with Putin was being set up.

Waltz said preparations are underway for the summit meeting and he expects a call between the leaders at least in the coming days and weeks.

Turning to Ukraine, Waltz noted that Ukrainians have manpower issues and their troop shortage needs to be addressed. He suggested that Ukraine lower its draft age from 25 to 18.

Waltz said: "Everybody knows that this has to end somehow diplomatically. I just don't think it's realistic to say we're going to expel every Russian from every inch of Ukrainian soil, even Crimea."

He also said Trump has acknowledged that reality.