WASHINGTON — The Trump administration announced new sanctions on Wednesday against three organizations and an individual accused of facilitating illicit shipments to North Korea, keeping pressure on the government of Kim Jong-un amid ongoing negotiations over the dismantling of his nuclear program.

The companies targeted by the Treasury Department are based in China, Singapore and Russia. The shipments, which violate sanctions imposed by the United States and the United Nations, include exports of alcohol, tobacco and cigarette products, as well as refined oil products.

“Treasury will continue to implement existing sanctions on North Korea, and will take action to block and designate companies, ports, and vessels that facilitate illicit shipments and provide revenue streams to the DPRK,” Steven Mnuchin, the Treasury secretary, said in a statement, using initials for North Korea’s official name.

“The tactics that these entities based in China, Singapore, and Russia are using to attempt to evade sanctions are prohibited under U.S. law, and all facets of the shipping industry have a responsibility to abide by them or expose themselves to serious risks,” Mr. Mnuchin said.