Trump slams 'haters' over Russia, takes dig at Kim for calling him 'old'

US President Donald Trump unleashed a twitter storm from his Asia tour today, slamming "haters and fools" playing politics with US-Russia ties and declaring that he would never describe North Korean leader Kim Jong-Un as "short and fat".

Currently on the Vietnam leg of a five-nation sweep through the region, the US president, who has been relatively quiet on Twitter since leaving Washington, put out half-a- dozen tweets in quick succession ahead of his official welcoming ceremony in Hanoi.

The missives covered a range of subjects from Trump's relations with Russian President Vladimir Putin, China's efforts to rein in Pyongyang's nuclear weapons programme, and a sarcastic tweet about his efforts to make "a friend" of North Korean leader Kim Jong-Un.

The US president, who met with Putin several times on the margins of the just-concluded APEC summit in the Vietnamese resort of Danang, took a fresh swipe at critics of his efforts to forge a close working relationship with the Russian leader.

"When will all the haters and fools out there realise that having a good relationship with Russia is a good thing, not a bad thing", he tweeted.

"There (sic) always playing politics - bad for our country. I want to solve North Korea, Syria, Ukraine, terrorism, and Russia can greatly help!" he added.

Speaking to reporters on Air Force One while flying to Hanoi on Saturday, Trump said he believed Vladimir Putin was being sincere when he denied meddling in the 2016 US presidential election.

Trump, whose key former aides are under the US investigation for possible collaboration with the Kremlin, said he had repeatedly asked Putin about the claims during their chats in Danang.

"He (Putin) said he didn't meddle. I asked him again", Trump, who is marking one year since his shock election victory, told the reporters.

"I really believe that when he tells me that, he means it," he added.

Trump's Sunday morning tweets also focused on North Korea and its nuclear weapons ambitions that have been a dominant theme on each leg of his Asia tour.

Taking exception to descriptions by North Korean officials and state media of him as an "old" man, Trump declared himself disappointed by what he took to be a personal attack from the North's young leader.

"Why would Kim Jong-un insult me by calling me "old," when I would NEVER call him "short and fat?" Trump said.

"Oh well, I try so hard to be his friend - and maybe someday that will happen!" he added.

North Korea is extremely sensitive to any remarks, even if not meant seriously that it sees as disrespectful of the country' ruling Kim dynasty, whose members are revered as near deities.

Since becoming president, Trump has engaged in an escalating war of words with Kim, trading personal insults and threats of military strikes and raising concerns about an outbreak of hostilities.