The U.S. tightened its financial restrictions on North Korea, slapping sanctions on Chinese and Russian entities it accused of assisting Pyongyang’s development of nuclear weapons and ballistic missiles, and also seeking millions of dollars it said moved through the U.S.

Prosecutors in Washington, D.C., sought to recover $11 million from companies based in China and Singapore that they accused of conspiring with North Korea to evade sanctions. In complaints filed Tuesday in federal court in the District of Columbia, they accused the companies of laundering dollars through U.S. accounts on behalf of sanctioned entities in North Korea.

“These complaints show our determination to stop North Korean sanctioned banks and their foreign financial facilitators from aiding North Korea in illegally accessing the United States financial system to obtain goods and services in the global market place,” said U.S. Attorney Channing D. Phillips. “According to the complaints, these front companies are supporting sanctioned North Korean entities, including North Korean military and North Korean weapons programs.”

Earlier Tuesday, the U.S. Treasury added more than a dozen individuals and companies to its roster of blacklisted North Korea-related entities, an escalation of the Justice Department’s focus on tightening sanctions against Pyongyang.

Treasury’s Office of Foreign Assets Control added six individuals and 10 companies and other entities to its sanctions list, saying they have helped people previously penalized for North Korea’s weapons development, facilitated North Korea’s energy sector and enabled entities to bypass sanctions to get access to the U.S. and international financial system.

The new restrictions seek to further reduce the flow of money to North Korea’s weapons development, which is partially financed by selling coal and other natural resources. North Korea generates about $1 billion a year from the coal trade, according to the Treasury, which singled out three Chinese coal companies it said was responsible for importing almost a half-billion dollars in North Korean coal between 2013 and 2016.

“Treasury will continue to put pressure on North Korea by targeting those who support the advancement of nuclear and ballistic missile programs and isolating them from the American financial system,” Treasury Secretary Steven Mnuchin said in a statement accompanying the sanctions announcement.

Read a QuickTake on North Korea’s nuclear weapons program

As part of the announcement, three Russian individuals and two Singapore-based companies were accused of providing oil to North Korea.

The sanctions are the latest against third-country companies and individuals in an effort to exert greater economic pressure on Kim Jong Un’s regime, which has conducted regular missile and nuclear tests in defiance of United Nations resolutions and has developed weapons that may be capable of hitting the continental U.S.

President Donald Trump has sought to pressure China — North Korea’s top trading partner — to use greater leverage on its neighbor and ally, though Kim’s regime often makes decisions contrary to Beijing’s wishes.