Secretary of State Mike Pompeo's statement follows UN report of numerous violations
US calls for keeping up sanctions pressure on North Korea
US Secretary of State Mike Pompeo called on Saturday for pressure to be maintained on North Korea as a UN report warned that Pyongyang was circumventing tough sanctions imposed over its nuclear weapons programme.
In Singapore for a regional security forum, Mr Pompeo said he had urged other countries to strictly enforce United Nations sanctions against North Korea, which appears to have made slow progress towards denuclearisation following a pledge at a landmark June summit.
He singled out Russia after reports suggested they were breaching sanctions and said China — one of Pyongyang's few allies — had vowed to enforce the measures.
Mr Pompeo said he had "emphasised the importance of maintaining diplomatic and economic pressure on North Korea to achieve the final, fully verified denuclearisation that DPRK has agreed to", using the initials of the North's official name.
"I must say from my meetings here, the world is united in seeing this achieved," Mr Pompeo told a press conference.
"We're determined to do it, Chairman Kim is committed to doing it. I'm optimistic that we will get this done."
As ministers gathered for a photo at the meeting, Mr Pompeo went over to greet North Korean Foreign Minister Ri Yong Ho, with the pair shaking hands, exchanging smiles and a few words.
Mr Pompeo has travelled to the North several times in recent months, including in July as he sought to flesh out Pyongyang's denuclearisation commitment.
His comments came as a UN report said North Korea had resorted to a "massive increase" of ship-to-ship transfers of oil products at sea to evade sanctions.
The 62-page report sent to the Security Council also listed violations of a ban on North Korean exports including coal, iron and seafood that generate millions of dollars in revenue for the reclusive regime.
At the summit with President Donald Trump in June, the North's leader Kim Jong-un signed up to a vague commitment to "denuclearisation of the Korean Peninsula" — a far cry from long-standing US demands for complete, verifiable and irreversible disarmament.
While there have been small signs of progress, news reports indicate Pyongyang is continuing to build rockets and there have been concerns that some countries are relaxing the enforcement of sanctions.
There has been no clear indication how long it will take the North to disarm or how exactly it will do so, and Mr Pompeo said in Singapore that the timing would be up to Mr Kim.
"The ultimate timeline for denuclearisation will be set by Chairman Kim, at least in part," he told local broadcaster Channel NewsAsia. "The decision is his."
At Saturday's press conference, Mr Pompeo said the US was "heartened" by Pyongyang's recent return of the remains of dozens of American soldiers killed during the Korean War.
But he also warned that Washington would take the infringement of sanctions by other countries "very seriously".
"We have seen reports that Russia is allowing for joint ventures with North Korean firms and granting new work permits to North Korean guest workers," he said. "If these reports are proven accurate, and we have every reason to believe that they are, that would be in violation" of UN sanctions.
Mr Pompeo said that during his meetings in Singapore, he called specifically for countries to enforce sanctions by stopping ship-to-ship transfers of petrol.
Cutting off oil and fuel to the North would require enforcement primarily by China, which supplies most of North Korea's energy needs, but also by Russia, which delivers some oil to Pyongyang.
The US top diplomat said that in talks on Friday, Chinese Foreign Minister Wang Yi was clear on Beijing's "continued commitment" to enforce sanctions.
Mr Pompeo also held talks with his counterparts from South Korea and Japan.
Saturday's forum, hosted by the Association of Southeast Asian Nations, brings together top diplomats from 26 countries and the European Union for talks on political and security issues in the Asia-Pacific.
Mr Wang met the North's foreign minister in Singapore and praised Pyongyang's "efforts in promoting the denuclearisation process", China's official Xinhua news agency said.
Mr Ri will visit Iran after the Singapore meeting, according to North Korea's KCNA news agency.
North Korea is reported to have a history of co-operation in military and missile technology with Iran, whose nuclear drive also sparked international alarm.