Donald Trump has said he is hitting North Korea with its “heaviest sanctions ever” and could move to “phase two” if they do not work.
The campaign will put “maximum pressure” on the regime to reduce its weapons programme, he told the Conservative Political Action Conference (CPAC) just outside Washington on Friday.
“We imposed today the heaviest sanctions ever imposed on a country before,” he said.
Treasury Secretary Steve Mnuchin confirmed the sanctions covered “virtually all the ships” North Korea is “using at this moment in time”.
“The President has made it clear to companies worldwide that if they choose to help fund North Korea’s nuclear ambitions, they will not do business with the United States,” he warned.
More than 450 sanctions have been imposed on North Korea, Mr Mnuchin said.
Mr Trump had been expected to provide details of measures which target “56 vessels, shipping companies, and trade businesses” registered in countries including China, Singapore, Tanzania, Panama and North Korea.
He did not go into greater detail during his address at CPAC, but said: “Frankly hopefully something positive can happen.”
Several Chinese-registered ships have been seized for secretly siphoning off oil to North Korean ships in international waters over the past few months.
Despite this, Japan reported “suspicious activity” between Chinese and North Korean ships on Wednesday.
During a press conference with Australian Prime Minister Malcolm Turnbull, Mr Trump said sanctions were only the first stage.
“If the sanctions don’t work, we’ll have to go to phase two. Phase two may be a very rough thing,” he said, without elaborating further.
The US is fighting North Korea’s nuclear ambitions with sanctions over fears a long-range missile could reach major US cities.
The latest sanctions are designed to place pressure on North Korea’s economy and fuel supply – both of which are already precarious.
Mr Mnuchin said the sanctions are already having an impact.
Beijing has warned against a full oil embargo on the North over fears of Kim Jong Un’s regime collapsing.
However, it has agreed to caps set by the UN.