"Absolutely ... You will continue without a doubt to see more from this administration," Sigal Mandelker, US Treasury Under Secretary for Terrorism and Financial Intelligence told a Senate hearing when asked if more sanctions were forthcoming.

"We have imposed major costs on Russia," she told the Senate Banking Committee.

"We believe its adventurism undoubtedly has been checked by the knowledge that we can bring much more economic pain to bear using our authorities -- and that we will not hesitate to do so if its conduct does not demonstrably and significantly change."

The statement came shortly after the Treasury slapped punitive sanctions on two Russian shipping firms and six Russian-flagged vessels linked to the firms for violating economic sanctions on North Korea.

The Treasury said Primorye Maritime Logistics Co. and Gudzon Shipping Co. own a tanker, the M/V Patriot, which conducted ship-to-ship transfers of oil to North Korea tankers twice earlier this year.

That violated a UN-backed embargo on doing business with North Korea (DPRK), part of an effort to pressure Pyongyang to give up its nuclear weapons and ballistic missiles 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," Treasury Secretary Steven Mnuchin said in a statement.

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

The sanctions freeze any of the companies' assets in US jurisdiction and severely restrict their access to the global financial system.

The US has blacklisted numerous major Russian corporations and powerful figures, both from government and business, in the circle of President Vladimir Putin.

Mandelker said Russia's continuing "malign activity" around the world -- interfering with US elections, supporting the Assad regime in Syria, using chemical weapons in an assassination attempt in Britain, and violating its own citizens' human rights -- requires the US to keep up pressure.

Also on Tuesday Microsoft announced that it had shut down six fake websites set up by Russia's GRU intelligence designed to redirect traffic from two US conservative thinktanks and the US Senate.

Mandelker said the sanctions have had a hefty impact on the Russian economy, cutting foreign investment and slashing the wealth of the billionaire oligarchs close to Putin.

"Targeting these Russian individuals and entities have made them radioactive, as we have made clear to the world that those who choose to do business with them do so at their own peril," she said.