The United States on Nov. 21 imposed sanctions against 13 Chinese and North Korean organizations Washington accused of helping evade nuclear restrictions against Pyongyang and supporting the country through trade of commodities like coal.

The U.S. Treasury announced the action one day after President Donald Trump put North Korea back on a list of state sponsors of terrorism, on its website.

The new curbs show the Trump administration's focus on hurting trade between China and North Korea, which it sees as key to deterring Pyongyang from its ambition to develop a nuclear-tipped missile capable of hitting the United States.
"This designation will impose further sanctions and penalties on North Korea and related persons, and supports our maximum pressure campaign to isolate the murderous regime," said Treasury Secretary Steven T. Mnuchin.
The latest sanctions included blacklisting three Chinese companies, Dandong Kehua Economy Trade Co., Dandong Xianghe Trading Co., and Dandong Hongda Trade Co., which the Treasury Department said had done more than $750 million in combined trade with North Korea over almost five years until Aug. 31.
It said they were involved in trade of coal, iron ore, lead, zinc and silver ore, lead metal and ferrous products as well as notebook computers.
The sanctions also blacklisted Sun Sidong and his company Dandong Dongyuan Industrial Co. In a June report, Washington think tank C4ADS said the firm was part of an interconnected network of Chinese companies that account for a vast share of trade with North Korea.
U.S. authorities have repeatedly targeted companies and individuals from the Chinese city of Dandong, which borders North Korea, in a bid to cut off Pyongyang's major export revenue from selling natural resources, such as coal.
The direct impact on listed companies may be limited as trade between China and its isolated northern neighbor has slowed substantially since the United Nations imposed a ban in September on North Korean exports of coal, iron, iron ore, lead, lead ore and seafood.
In February, China also prohibited coal purchases from North Korea.
 
Meanwhile, Air China has suspended flights to North Korea, further limiting the secretive state's links with the outside world, in what the government said was a business decision with no political motives.
 
China sent a special envoy, Song Tao, to the North last week but his four-day trip ended with no direct statement on the crisis, after Pyongyang's series of nuclear and missile tests triggered global alarm.
 
Air China said in a statement to AFP that it cancelled the Beijing to Pyongyang flight route because the "operational situation is not ideal."
 
"Market conditions will determine the resumption of the flight route," the statement said.