The United States said on Friday it was imposing its largest package of sanctions to pressure North Korea to give up its nuclear and missile programmes.
President Donald Trump warned of a "phase two" that could be "very, very unfortunate for the world" if the steps did not work.
In addressing the Trump administration's biggest national security challenge, the US Treasury sanctioned one person, 27 companies and 28 ships, according to a statement on the US Treasury Department's website.
The United States also proposed a list of entities to be blacklisted under separate UN sanctions, a move "aimed at shutting down North Korea's illicit maritime smuggling activities to obtain oil and sell coal".
North Korea has been developing nuclear-tipped missiles capable of reaching the US mainland and Mr Trump and North Korean leader Kim Jong-un have exchanged taunts that have raised fears of war.
- What Jacinda Ardern thought of Donald Trump's 'short and fat' tweet
- Thousands fall for satirical Donald Trump 'gorilla channel' tweet
- Trump warns North Korea of 'fire and fury' after threats
In August, Mr Trump threatened to go beyond sanctions by bringing "fire and fury like the world has never seen", although his administration has repeatedly said it prefers a diplomatic solution to the crisis.
Speaking at a news conference with Australian Prime Minister Malcolm Turnbull, Mr Trump made apparent reference to military options his administration has repeatedly said remain on the table.
"If the sanctions don't work, we'll have to go phase two," Mr Trump said. "Phase two may be a very rough thing, may be very, very unfortunate for the world. But hopefully the sanctions will work."
The sanctions' targets include a Taiwan passport holder, as well as shipping and energy firms in mainland China, Hong Kong, Taiwan and Singapore. The actions block assets held by the firms and individuals in the United States and prohibit US citizens from dealing with them.
The US Treasury said the sanctions were designed to disrupt North Korean shipping and trading companies and vessels and further isolate Pyongyang. They are also aimed at ships located, registered or flagged in North Korea, China, Singapore, Taiwan, Hong Kong, Marshall Islands, Tanzania, Panama and the Comoros.
Last month, three Western European intelligence sources told Reuters that North Korea shipped coal to Russia last year and that it was then delivered to South Korea and Japan in a likely violation of UN sanctions.
China's response
China's foreign ministry is demanding the US stop enacting unilateral sanctions against Chinese entities and individuals, after Washington said it was imposing its largest package of sanctions to pressure North Korea.
China has lodged "stern representations" with the US over the sanctions, whose targets include a Taiwan passport holder, as well as shipping and energy firms in mainland China, Hong Kong, Taiwan and Singapore.
China "demands the US side immediately stops such relevant mistaken actions to avoid harming bilateral cooperation in the relevant area", the ministry said in a short statement on Saturday.
Reuters
