US President Donald Trump says he is launching the "largest ever" set of new sanctions against North Korea.
The new measures will target 56 ships and maritime transport companies.
"Today I am announcing that we are launching the largest-ever set of new sanctions on the North Korean regime," Mr. Trump said in released sections of a speech to be delivered shortly.
North Korea is already under a range of international and US sanctions over its nuclear programme and missile tests.
"The treasury department will soon be taking new action to further cut off sources of revenue and fuel that the regime uses to fund its nuclear programme and sustain its military by targeting 56 vessels, shipping companies, and trade businesses that are assisting North Korea in evading sanctions," Mr. Trump said.
It is not yet clear where the ships or companies targeted are based.
The US has been building sanctions against the regime since 2008 and the latest restrictions could come on top of sanctions announced in November - directed at North Korean shipping operations, as well as Chinese companies trading with Pyongyang.
The United Nations followed that up in December with a raft of sanctions, backed by all 15 members of the Security Council, which included measures to cut North Korea's petrol imports by up to 90%.
Mr. Trump's announcement comes as North Korea conducts what is being seen by Western powers as a charm offensive at the Winter Olympics in South Korea.
US leaders have been keen to stress that North Korea still poses a nuclear threat despite warming ties with the South.
The president's wife, Melania, is in South Korea to attend the closing ceremony of the Games and Vice-President Mike Pence was there for the opening.
However, no meetings have taken place with senior North Korean officials attending, including Kim Yo-jong, sister of the North Korean leader Kim Jong-un.