Trump wants denuclearisation talks with Russia's Putin and China's Xi

US President Donald Trump has said he wants to hold talks with Russia and China on a mutual reduction in military spending, with a possible summit for the countries' leaders.

Outlining his vision for a shake-up in the world order, Trump also said on Thursday he would "love" to have Russia back in the G7, from which it was suspended in 2014 after Moscow annexed Ukraine's Crimea peninsula.

"I think it was a mistake to throw him out," Trump said, referring to Russian President Vladimir Putin.

Trump — who sees himself in his second term as a global peacemaker — also said he would consider a summit with Putin and China's Xi Jinping "when things calm down."

"When we straighten it all out, then I want one of the first meetings I have is with President Xi of China, President Putin of Russia. And I want to say, let's cut our military budget in half."

Speaking to reporters in the Oval Office, Trump lamented the hundreds of billions of dollars being invested in rebuilding the nation's nuclear deterrent and said he hopes to gain commitments from the US adversaries to cut their own spending.

"There's no reason for us to be building brand new nuclear weapons, we already have so many," Trump said. "You could destroy the world 50 times over, 100 times over. And here we are building new nuclear weapons, and they’re building nuclear weapons."

While the US and Russia hold massive stockpiles of weapons since the Cold War, Trump predicted that China would catch up in their capability to exact nuclear devastation "within five or six years."

Meeting with Putin

Trump made his comments at the White House after he inked plans for sweeping "reciprocal tariffs" that could hit both allies and competitors including India whose Prime Minister Narendra Modi is in Washington for talks.

In 2014, Russia was suspended from what was then the G8 after it annexed Crimea and sanctions were imposed on Moscow.

In his first term, Trump also called for Russia to be readmitted, but he found little support among other Western countries.

Trump revealed on Wednesday he expected to meet Putin separately for Ukraine peace talks in Saudi Arabia, in a sudden thaw in relations.

In their first confirmed contact since Trump's return to the White House, the US president said he had held a "highly productive" conversation with his Russian counterpart amid Moscow's ongoing Ukraine offensive.