The statement comes as six-party talks on ending North Korea's nuclear weapons programmes have become snagged over a US crackdown on firms it suspects of helping Pyongyang in illicit activities such as counterfeiting and money laundering.
Pyongyang has demanded Washington end what it sees as sanctions aimed at toppling its leaders in order for the talks to resume.
"We manufactured nuclear weapons with our own technology, funds and raw materials from A to Z. As we are not dependent on the US at all in the economic and financial fields, no US sanctions would work on us," a North Korean spokesman said on Tuesday.
"As we have clarified more than once, such illegal dealings as 'money laundering' and 'counterfeit notes' have nothing in common with the policy of the DPRK and such assertion of the US is nothing but a fabrication solely intended to tarnish the image of the DPRK and do harm to it," the spokesman said in response to a question by the North's KCNA news agency.
DPRK is an abbreviation of North Korea's official name, the Democratic People's Republic of Korea.
A South Korean MP shows what he
says is counterfeit US currency
Proliferation experts say the former Soviet Union helped North Korea start its nuclear programme.
US officials have charged that the nuclear black market network run by disgraced Pakistani scientist Abdul Qadeer Khan, supplied North Korea with technology to produce highly enriched uranium for nuclear bombs.
The United States has said it suspects North Korea used money from illicit activity to help finance its nuclear programmes. North Korea has denied involvement in illegal activities.
Washington, Seoul and others have said the crackdown is a separate issue from the nuclear talks and urged North Korea to return to the table. US officials said they have presented evidence of North Korean counterfeiting to various governments.
The fate of talks on North Korea's nuclear programmes depends on whether Pyongyang takes action on illicit activities that prompted a US crackdown, the former head of the South Korean delegation to the six-party talks told local media recently.
North Korea, which has an anaemic economy and has had trouble repaying loans, blamed the United States for forcing it to make international transactions in cash.
"We manufactured nuclear weapons with our own technology, funds and raw materials from A to Z"
North Korean spokesman
Economists have said decades of economic mismanagement has been the reason for North Korea ranking near the bottom in the world in terms of per capita gross domestic product.
"The US has completely barred us from having normal financial transactions such as remittance of dollars to banks and settlement by credit cards," the spokesman said.
The spokesman blasted "the US for persistently floating far-fetched assertion that the DPRK counterfeited US dollars without producing any evidence".