The network is alleged to have helped North Korea with procuring items for its ballistic missile programs, which the US Treasury Department said were being operated in "flagrant violation" of UN Security Council resolutions.

North Korea's continued development of its ballistic missile technologies "is both irresponsible and destabilizing for both the region and the international community," Treasury under secretary for terrorism and financial intelligence Brian Nelson said in a statement.

"The United States remains committed to using our tools to enforce these international sanctions, including disrupting the illicit procurement networks that provide key inputs for these technologies," he added.

Beijing's foreign ministry hit back Thursday, saying it "opposes illegal unilateral sanctions."

"China always conscientiously implements UN Security Council resolutions and fulfils its own international obligations, and is committed to upholding peace and stability on the (Korean) peninsula," ministry spokeswoman Mao Ning said at a news conference.

"Indiscriminately imposing sanctions cannot resolve peninsular issues," she said.

The US Treasury said North Korea's space and ballistic missile programs made use of an "extensive network" of overseas agents to procure the foreign-sourced materials needed, which included personnel at its diplomatic missions and trade offices, "as well as third-country nationals."

It also makes use of foreign firms to purchase the items it needs, the Treasury added.

Among those sanctioned on Wednesday was Shi Qianpei, a Chinese national, whom the Treasury accused of working with a previously-designated individual based in Beijing to procure metal sheets used in the production of North Korean missiles.

Other individuals sanctioned include Chen Tianxin, Shi Qianpei's business partner and wife, and two of his employees, all of whom helped with the procurement efforts, the Treasury said.