North Korea has warned the United States of "unimaginable consequences" from its "hostile" policy toward the nuclear armed state, urging Washington to accept its long-standing demand for a peace treaty.

The warning was made in a statement from the North's foreign ministry late Wednesday in reaction to fresh sanctions imposed by Washington last week.

The sanctions would "only heighten the spirit of self-reliance and increase the strenuous efforts" among the workers of its munitions industry and boost the proportion of materials for weapons production, the foreign ministry spokesman said.

"If the US persistently pursues its anachronistic hostile policy toward the DPRK (North Korea) this way, this would only entail unimaginable consequences quite contrary to what the US desires," the spokesman was quoted as saying by Pyongyang's state Korean Central News Agency.

He did not elaborate on the "unimaginable consequences", stopping short of reiterating Pyongyang's habitual threats to bolster its nuclear arsenal.

The spokesman also urged "the conclusion of the peace treaty with the US in order to put an end to the hostile policy", which he said was "the root cause of all problems".

"Lasting peace and stability are possible on the Korean Peninsula only when the US hostile policy toward the DPRK is brought to an end and hostile relations between them are defused", he said.

The United States last week imposed financial sanctions against six North Korean individuals and several companies linked to arms proliferation.

They included North Korea's Strategic Rocket Force, which had carried out multiple ballistic missile tests in 2014, two banks and three shipping companies allegedly involved in the arms trade, according to the US Treasury.

The sanctions bar American citizens or companies from engaging in transactions with the designated individuals and companies, and freezes any US-based assets they may have.