US Secretary of State Rex Tillerson on Thursday urged China to use the oil it supplies to North Korea as leverage to pressure the isolated nation into reconsidering its nuclear programme.
The UN Security Council unanimously imposed on Monday an eighth set of sanctions on North Korea after its latest nuclear test, banning it from trading in textiles and restricting oil imports.
Washington had called for tougher restrictions, including an oil embargo, in response to Pyongyang's sixth and most powerful nuclear blast.
But the US softened its stance in order to secure the backing of China and Russia, which could have vetoed the proposal.
"It's clear with respect to oil and a complete embargo from the Security Council, that's going to be very difficult," Tillerson said, standing alongside his UK counterpart Boris Johnson.
The US secretary of state said it would be up to China alone to decide "to use the very powerful tool of oil supply to pressure North Korea" into reconsidering its approach to dialogue.
Johnson said sanctions were a way of "maximising the pressure on North Korea to reach a diplomatic solution", calling for the "complete and irreversible" denuclearisation of the Korean peninsular.
- Iran deal -
While North Korea was top of the agenda during Tillerson's visit to London, he also touched upon the 2015 Iran nuclear deal in a meeting with British Prime Minister Theresa May.
"The prime minister underlying its importance in preventing Iran from procuring nuclear weapons," May's spokesman said.
"Full implementation of JCPOA (the Iran deal) would positively contribute to regional and international peace and stability," Tillerson said.
But he cautioned that Iran was "clearly in default of the expectations" in Washington of the 2015 accord.
The US on Thursday took action against 11 individuals and companies accused of supporting Iran's Revolutionary Guards or engaging in cyber attacks against US banks, imposing economic sanctions.
Tillerson and Johnson also discussed the response to Hurricane Irma, which raged through the Caribbean last week and also struck the US, and the situation in Libya.
- Myanmar violence -
Turning to Asia, the US secretary of state addressed the "unacceptable" violence against Rohingya Muslims in Myanmar, as thousands of refugees continue to stream across the border into Bangladesh.
"We need to support Aung San Suu Kyi and her leadership but also be very clear and unequivocal to the military power sharing in that government that this is unacceptable," Tillerson said.
"This violence must stop. This persecution must stop. It has been characterised by many as ethnic cleansing. That must stop," he said.
"I think it is a defining moment in many ways for this new emerging democracy," Tillerson said, acknowledging that Myanmar's leader Suu Kyi found herself in a "difficult and complex situation".
Johnson also called on Myanmar's de facto leader to use her "moral capital" to highlight the plight of the Rohingyas.
"I think nobody wants to see a return to military rule in Burma, nobody wants to see a return of the generals," he said.
"It is vital for her now to make clear that this is an abomination and that those people will be allowed back" in the country, he added.
A crackdown by Myanmar's army, launched in response to attacks by Rohingya militants on August 25, has pushed vast numbers of refugees from the stateless Muslim minority across the border.
Some 389,000 are estimated to have crossed since then.