US President Donald Trump said on Sunday that he was available to mediate between claimants in territorial disputes in the South China Sea.

“If I can help mediate or arbitrate, please let me know,” Trump said in comments at the beginning of a meeting in Hanoi with Vietnam’s president, Tran Dai Quang, in the wake of the just-concluded APEC summit in the Vietnamese resort of Danang.

Trump acknowledged that China’s position on the South China Sea – nearly all of which is claimed by Beijing – is a problem. “I’m a very good mediator and arbitrator,” he said.

He also said that China was helping to resolve tensions over North Korea and added he hoped Russia would do the same.

Trump also promised a “tremendous amount of trade” with Vietnam as he and Quang spoke briefly to reporters.

Earlier, the US president indulged in a fresh Twitter assault, slamming “haters and fools” who question his efforts to improve ties with Russia and taking a dig at North Korea’s “short and fat” leader, Kim Jong-Un.

Having been relatively quiet on Twitter since leaving Washington on a five-nation tour of Asia just over a week ago, Trump put out half a dozen tweets in quick succession before meeting Quang.

The missives covered a range of targets and subjects – from the critics of his desire for a close relationship with Russian President Vladimir Putin to China’s efforts to rein in Pyongyang’s nuclear weapons program.

“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 wrote, having met with Putin several times on the margins of the Danang summit.

“[Putin] said he didn’t meddle. I asked him again. I really believe that when he tells me that, he means it.”

“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 had said he believed Putin was being sincere when he denied meddling in the 2016 US presidential election.

Trump, whose key former aides are under 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,” Trump said. “I asked him again. I really believe that when he tells me that, he means it.”

In May, US intelligence chiefs told Congress they agreed with their analysts’ conclusion that Russia had meddled in the election. And in January, 17 US intelligence agencies took the extraordinary step of stating publicly that they believed Russia did try to interfere.

‘Short and fat’

Trump’s Sunday tweets also focused on North Korea and its nuclear weapons ambitions.

Taking exception to descriptions by North Korean officials and state media of him as an “old” man, Trump indicated he was 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 known to be extremely sensitive to remarks – even when delivered in tongue-in-cheek fashion meant seriously – that might appear disrespectful of the country’s ruling Kim dynasty.

Over the past week, Trump has urged Asian leaders to take a united stand against the threat posed by the pariah state, warning at APEC that the region “must not be held hostage to a dictator’s twisted fantasies.”

In another tweet on Sunday, Trump said Chinese leader Xi Jinping had agreed to toughen sanctions against North Korea, whose impoverished economy is hugely reliant on trade with its giant neighbour.

“President Xi of China has stated that he is upping the sanctions against (North Korea). Said he wants them to denuclearise. Progress is being made,” he wrote.

Reporting from Reuters, Agence France-Presse