The department also sanctioned two Taiwanese individuals and designated a Panama-flagged vessel as blocked property for engaging in related activity.

"Shipping companies trading with North Korea are exposing themselves to significant sanctions risk, despite the deceptive practices they try to employ," Treasury Under Secretary Sigal Mandelker said in a statement.

"Treasury will implement and enforce existing US and UN sanctions on individuals, entities and vessels involved in illicit ship-to-ship transfers with North Korean flagged vessels," she added.

North Korea is under a wide array of international sanctions for its nuclear and ballistic missile programs, including a UN-imposed cap on imports of refined petroleum products.

The regime has been accused of conducting illicit ship-to-ship transfers at sea to evade such restrictions.

The US has vowed to continue sanctions against the North until the regime dismantles its nuclear program, and the latest action comes as denuclearization negotiations between the sides have stalled.

The three companies are Jui Pang Shipping and Jui Zong Ship Management, based in Taiwan, and Jui Cheng Shipping, based in Hong Kong.

The two individuals, Huang Wang Ken and Chen Mei Hsiang, are married and work as the CEO and a member of the board of directors of Jui Pang, respectively, according to the Treasury. Chen is also the director and sole owner of Jui Zong.

The Treasury said Huang and others used the Panama-flagged vessel, Shang Yuan Bao, to conduct at least two transfers with North Korean vessels in 2018.

More than 1.7 million liters of petroleum products were thus transferred to North Korea, but Huang and his partners falsely reported the products were destined for the Philippines, it said.

North Korea is currently allowed to import 500,000 barrels, or nearly 80 million liters, of refined petroleum products per year.

At the second summit between US President Donald Trump and North Korean leader Kim Jong-un in February, the North asked that the US remove such sanctions in exchange for the dismantlement of its main nuclear complex in Yongbyon.

The US rejected the offer and the summit ended without a deal.

For six months, the two sides have not held formal negotiations despite an agreement between Trump and Kim in June to resume them within several weeks.

In a recent statement, North Korean Foreign Minister Ri Yong-ho warned that the US would be "sadly mistaken" if it planned to continue its "confrontation" with the North through sanctions.

The new measures freeze the property and interests of the designated individuals and entities in the US and ban their financial transactions with American citizens.