WASHINGTON -- The United States on Tuesday sanctioned two Russian shipping companies and six Russian vessels for allegedly helping North Korea's illicit activities in violation of international sanctions.

The Department of the Treasury announced that the sanctions target persons involved in the banned ship-to-ship transfer of refined petroleum products to North Korea-flagged vessels.

The designated entities will now have any property or interests in the US frozen, including dealings with US citizens.

It is the third time this month that Washington has slapped sanctions on Russian firms for their alleged ties to illegal North Korean activity, demonstrating again the US commitment to keep pressure on Pyongyang until it abandons its nuclear weapons and ballistic missile programs.

"Ship-to-ship transfers with North Korea-flagged vessels from Russia or elsewhere of any goods being supplied, sold, or transferred to or from the DPRK are prohibited under the UN Security Council resolutions on North Korea and are sanctionable under US law," Treasury Secretary Steven Mnuchin said in a statement, referring to North Korea by its official name, the Democratic People's Republic of Korea.

"Consequences for violating these sanctions will remain in place until we have achieved the final, fully verified denuclearization of North Korea," he said.

The action targets Primorye Maritime Logistics and Gudzon Shipping, both based in Vladivostok, Russia, as well as six Russia-flagged vessels, including five identified as linked to Gudzon.

The sixth vessel, PATRIOT, is linked to both Primorye and Gudzon, and is accused of conducting two ship-to-ship oil transfers to two sanctioned North Korea-flagged vessels early this year.

The shipments were ultimately bought by North Korea's Taesong Bank, which is believed to be under the UN- and US-sanctioned Office 39 of the ruling Workers' Party of Korea, the Treasury said.

It described Office 39 as engaging in "illicit economic activities for (the) North Korean leadership."

The series of sanctions come despite an agreement between US President Donald Trump and North Korean leader Kim Jong-un at their historic summit in June to improve bilateral relations.

Kim also committed at the summit to work toward the "complete denuclearization" of the Korean Peninsula in exchange for security guarantees from the US.

The US has vowed to keep sanctions on the regime until the North fully abandons it nuclear program.

Speaking at the United Nations last month, US Secretary of State Mike Pompeo urged the international community to strictly enforce the established measures.

The UN Security Council last year passed a series of resolutions sanctioning the North for its sixth test of a nuclear weapon and multiple tests of ballistic missiles capable of reaching the US.

The actions banned exports of North Korean raw commodities and capped the regime's imports of oil in a bid to stop the flow of revenue and resources needed to develop the nuclear weapons and ballistic missile programs.

Pompeo said North Korea continues to smuggle oil products into the country through illegal ship-to-ship transfers, adding there were at least 89 such cases in the first five months of the year. (Yonhap)