However, on Tuesday the South Korean newspaper Chosun Ilbo cited unidentified South Korean government officials as saying US reconnaissance satellites have spotted Chinese ships transferring oil to North Korean vessels some 30 times since October in seas off China.
A senior administration official told CNN that the Trump administration is planning to be "more quiet" and "more discreet" about speaking publicly on United States military exercises with the Republic of Korea and Japan aimed at demonstrating military capability against North Korea.
China accounts for the vast majority of North Korea's external trade and oil supplies. That report was picked up by some US media outlets, including Fox News.
While Russia exports some oil to North Korea, China is the main source of oil for the rogue nation, according to Reuters.
The U.N. resolution seeks to ban almost 90 per cent of refined petroleum exports to North Korea by capping them at 500,000 barrels a year.
A spokeswoman for China's foreign ministry said Wednesday China has strictly enforced trade restrictions.
"As North Korea continues to threaten worldwide peace and security, we are steadfast in our determination to maximize economic pressure to isolate it from outside sources of trade and revenue while exposing its evasive tactics", Treasury Secretary Steve Mnuchin said at the time.
Members of the Trump administration have repeatedly vowed to stop North Korea's nuclear program - and have not ruled out a military option that some analysts fear could lead to a nuclear conflict.
The US-drafted resolution bans the supply of almost 75 percent of refined oil products to North Korea, puts a cap on crude deliveries and orders North Korean nationals working overseas to be sent back by the end of 2019.
On Thursday, China insisted that it was in full compliance with the resolution, as well as the new UN Security Council resolution passed last week, which places even tighter restrictions on North Korea's energy imports. The US Treasury Department later placed six North Korean shipping and trading companies and 20 of their vessels on sanctions list.
"China has applied certain import bans and sanctions, but it could and should do more", he wrote in The New York Times.