The United States has imposed new sanctions on Chinese and Russian firms and individuals for what it said was their support of North Korea's weapons programme - a move criticised by both Beijing and Moscow.

The US Treasury designated on Tuesday six Chinese-owned entities, one Russian, one North Korean and two based in Singapore.

They included a Namibia-based subsidiary of a Chinese company and a North Korean entity operating in Namibia.

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The sanctions also targeted six individuals - four Russians, one Chinese and one North Korean.

The measures block any assets individuals and entities may have in US jurisdictions and bar Americans from transactions with them.

"It is unacceptable for individuals and companies in China, Russia, and elsewhere to enable North Korea to generate income used to develop weapons of mass destruction and destabilize the region," Treasury Secretary Steven Mnuchin said in a statement.

Banks excluded

The move follows a war of words between Washington and Pyongyang over recent missile tests that show North Korea is capable of reaching the US mainland.

China reacted with irritation, saying Washington should "immediately correct its mistake" of imposing unilateral sanctions on Chinese companies and individuals to avoid damaging bilateral cooperation.

Russia also criticised criticized the US sanctions, with Deputy Foreign Minister Sergei Ryabkov saying that Kremlin was "starting to work on retaliatory measures, which are unavoidable in this situation".

The latest US steps stopped short of targeting Chinese financial institutions dealing with North Korea, a step that would have greatly angered Beijing.

The Trump administration is still hoping China will pressure Pyongyang.

"The sanctions target a range of North Korea's illicit activities and the focus on Chinese facilitators is another message to Beijing," Anthony Ruggiero, a Foundation for Defense of Democracies senior fellow and former US Treasury official, told the Reuters news agency.

"However, there are missing elements. There's no focus on the efforts of Chinese banks that facilitate these transactions. In addition, these Chinese networks likely have additional front companies operating on behalf of the network and those were not sanctioned."

Richard Nephew of Columbia University said it appeared the US government was "exploring what the tolerance is to the use of secondary sanctions."

"The fact that they've not yet moved forward with any big bank effort suggests to me that they're quite nervous about the risks of blowback and reasonably so," he told Reuters.