US President Donald Trump has offered Asia his services as a mediator, shortly after tweeting insults.

At the start of a meeting in Hanoi with the Vietnamese president, Mr Trump said he could help arbitrate the regional South China Sea dispute, which includes Vietnam and China.

"I'm a very good mediator and arbitrator," he said.

It came shortly after he called North Korea's Kim Jong-un "short and fat" on Twitter.

China, Vietnam, the Philippines, Taiwan, Malaysia and Brunei all have competing claims to territory in the South China Sea.