WASHINGTON — North Korean and Chinese nationals are operating a multibillion-dollar money laundering scheme to help fund North Korea’s nuclear weapons program, the Justice Department said in an indictment unsealed Thursday, a case that underscores the Trump administration’s inability to halt Pyongyang’s nuclear weapons program through diplomacy.

       The department charged 28 North Koreans and five Chinese nationals of using a web of more than 200 shell companies to launder over $2.5 billion in assets through the international banking system.

       The government alleged that the money flowed back to North Korea’s primary, state-operated foreign exchange bank, the Foreign Trade Bank of the Democratic People’s Republic of Korea, also known as Josen Bank. The funds were then used to support the country’s weapons of mass destruction program.

       The charges are an acknowledgment that the United States has been unable to stop North Korea from building nuclear weapons by imposing economic sanctions and through President Trump’s attempts to broker an agreement with North Korea’s leader, Kim Jong-un.

       Mr. Kim met this week with his nation’s top military-governing body and discussed “new policies for further increasing” North Korea’s nuclear capabilities.

       Mr. Kim recently went three weeks without making any public appearances, sparking speculation that he had been ill.

       “Set forth at the meeting were new policies for further increasing the nuclear war deterrence of the country and putting the strategic armed forces on a high alert operation,” the North’s official Korean Central News Agency reported. “Taken at the meeting were crucial measures for considerably increasing the firepower strike ability of the artillery pieces of the Korean People’s Army.”

       Mr. Trump has said that he would use his relationship with Mr. Kim to deter the country from building more weapons, and the two met in Singapore in June 2018 and in Hanoi, Vietnam, in February 2019. But those meetings failed to produce any agreement ？on ？how to end North Korea’s nuclear weapons programs ？or how to ease sanctions against North Korea that had been imposed by the United Nations.

       The United States and North Korea agreed that the talks had failed, with the meeting in Hanoi ending abruptly with no resolution. But they disagreed about why they came to no agreement.

       “Sometimes you have to walk,” Mr. Trump said in Hanoi after the talks had broken down. He said that Mr. Kim’s offer to dismantle a nuclear facility in exchange for sanctions relief was “a dealbreaker.”

       Mr. Kim has overseen four underground nuclear tests and has pushed for North Korea to build more nuclear weapons and missile programs. The country under his rule also flight-tested three intercontinental ballistic missile tests in 2017.