President Donald Trump on Friday said he was cancelling sanctions imposed by his own Treasury Department to tighten international pressure on North Korea.

"It was announced today by the US Treasury that additional large scale Sanctions would be added to those already existing Sanctions on North Korea. I have today ordered the withdrawal of those additional Sanctions!" Trump tweeted.

He appeared to be referring to measures unveiled on Thursday that targeted two Chinese companies accused of helping North Korea to evade tight international sanctions meant to pressure Pyongyang into ending its nuclear weapons programme.

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They were the first new sign of pressure since talks between Trump and North Korean leader Kim Jong Un broke down in Hanoi less than a month ago.

"President Trump likes Chairman Kim and he doesn't think these sanctions will be necessary," the president's spokeswoman, Sarah Sanders, said.

On Thursday, Trump national security advisor John Bolton had tweeted that the sanctions were meant to put an end to "illicit shipping practices" by North Korea.

"Everyone should take notice and review their own activities to ensure they are not involved in North Korea's sanctions evasion," he said.

China complained, saying that it did enforce all UN resolutions and opposed "any country imposing unilateral sanctions and taking long-arm jurisdiction against any Chinese entity according to their own domestic laws."