WASHINGTON—The Trump administration is moving toward unilaterally tightening sanctions on North Korea, targeting Chinese companies and banks the U.S. says are funneling cash into Pyongyang’s weapons program.

Sharper rhetoric from high-ranking U.S. officials since North Korea’s July 4 ballistic missile test and recently unsealed court filings offer clues that the White House is ready to use its own powers to constrict the flow of cash to Kim Jung Un’s regime. U.S. officials have expressed a preference for collective action through the United Nations and support from China.

The Justice Department, in a federal-court case that was partly unsealed last week, pointed to “offshore U.S. dollar accounts” associated with a network of five companies linked to Chinese national Chi Yupeng. That included one of the largest importers of North Korean goods into China, Dandong Zhicheng Metallic Material Co.

Citing sources that included two North Korean defectors, the Justice Department said the so-called Chi Yupeng network hid transactions which helped finance North Korea’s military and arms programs.

That network isn’t under U.S. sanctions but analysts say it is a vital source of funds that can be choked off, in the same way the U.S. targeted another Chinese firm late last year, Dandong Hongxiang Industrial Development Co. Ltd. Some of the nearly two dozen Chinese banks that handled allegedly laundered money from Dangdong Hongxiang also could be targeted, analysts said. The company declined to comment at the time.

China’s Foreign Ministry didn’t respond to a request to comment and Mr. Chi and Dandong Zhicheng couldn’t be reached.

North Korea has resisted pressure for years and many experts question whether this time would be any different. Pyongyang has become proficient at evading sanctions, U.S. officials say, including by disguising its international trade and financial entities through firms in China.

The U.S. itself has almost no direct ties to North Korea after imposing wide-ranging bilateral sanctions in response to previous missile and nuclear tests.

China, North Korea’s chief trade partner, has resisted tightening the screws against its neighbor, concerned that it could provoke Pyongyang to lash out against America’s allies in the region or precipitate a collapse of the regime that sparks a flood of refugees, analysts say. The status quo has also provided China a buffer against U.S. power in Asia.

Since raising the pressure on North Korea requires targeting more Chinese firms, unilateral action risks fueling already strained tensions between Washington and Beijing. It could complicate Washington’s efforts to expand access for U.S. companies into the world’s most populous country and win Beijing’s support on other international issues, such as on cyber security and resolving conflicts in the Middle East.

The George W. Bush administration brought North Korea back to the negotiating table in 2007 after escalating sanctions but the administration then softened pressure and Pyongyang resumed its nuclear-weapons program. The Obama administration sanctioned North Korea but the effort failed to halt the program.

U.S. officials say the stakes are greater after last week’s missile launch revealed Pyongyang’s ability to put Alaska within reach and that current efforts will be more stringent than in the past.

The Threat From North Korea’s Missiles

Pyongyang has accelerated its tests of missiles and nuclear bombs as it tries to develop a nuclear-armed missile that could hit the U.S. mainland

Even before the July 4 launch, the Trump administration began trying to tighten sanctions to cut off “all illegal funds going to North Korea,” Treasury Secretary Steven Mnuchin said just days before the test. “We will continue to look at these actions and continue to roll out sanctions.”

Late last month the U.S. Treasury said it would cut off China’s Bank of Dandong from U.S. financial markets, saying North Korea was using bank accounts under false names and conducting transactions through banks in China, Hong Kong and Southeast Asia. Neither the Chinese Embassy in Washington nor the Bank of Dandong responded to requests for comment. The Treasury also added to its North Korea sanctions list two Chinese citizens accused of working for front companies designed to evade existing sanctions.

Trump administration officials have warned that North Korea’s latest missile test warranted an escalation in international pressure, seeking first collective action through the U.N. Security Council and urging Beijing to use its own powers as a close Pyongyang ally to stem cash flows there.

“The United States is prepared to use the full range of our capabilities to defend ourselves and our allies,” Nikki Haley, U.S. ambassador to the U.N., told the Security Council last week. Ms. Haley said past sanctions have proved insufficient.

U.S. Secretary of State Rex Tillerson said Friday that sanctions issued last week against Chinese entities are a measure of the administration’s resolve but that he preferred that Beijing act on its own to curb North Korea financing.

Mr. Tillerson said the U.S. would apply “calculated increases in pressure,” but that there was a limit to the administration’s “strategic patience.”

The Trump administration asked China to take action against a list of nearly 10 Chinese companies and individuals to curb their trading with North Korea following President Donald Trump’s Mar-a-Lago summit with Chinese leader Xi Jinping in April, senior U.S. officials said.

But U.S. officials say they have been disappointed by Beijing’s response. The topic will be a focus of high-level U.S.-China talks next week in Washington, Mr. Mnuchin said, adding that the two leaders discussed the issue in Germany this past weekend.

Failure to act more aggressively could not only embolden Pyongyang, but also the entities that help finance the regime, said Bruce Klingner, a former Central Intelligence Agency deputy division chief covering North Korea now at the Heritage Foundation think tank.

Many former U.S. diplomats, including Juan Zarate, the top sanctions diplomat in the Bush administration, say Washington must ratchet up the pressure on Chinese firms and banks. The U.S. has so far been wary of prodding Beijing too hard, given the wealth of other vital geopolitical issues on which the two powers cooperate, former U.S. officials and analysts said.

North Korea’s latest missile test changes the administration’s calculus, said Nicholas Eberstadt, a North Korea security expert at the American Enterprise Institute. He expects the White House to accelerate its sanctions against Chinese firms.

Sanctions experts say the Trump administration is looking to emulate the success of Iranian sanctions, which forced Tehran to the negotiating table and halt its nuclear weapons program.

Analysts and senior officials from two previous administrations say existing sanctions against North Korea have been elementary compared with the thicket of actions applied against Iran by the Obama administration. That pushed Iran into recession and persuaded it to negotiate, although many foreign-policy experts question the effectiveness of the subsequent deal the U.S. reached with Iran.

A central aim of the new strategy of freezing out a Chinese bank from the U.S. financial system is to chill transactions by other Chinese institutions. Access to U.S. financial markets and the dollar are critical for trade and finance around the globe. But for that effort to be perceived as credible, said Mr. Eberstadt, the administration will have to list other Chinese banks to instill broader fear.

“If I wanted to send a message, I’d probably send several postcards,” Mr. Eberstadt said.

But while enhanced pressure could complicate Washington’s already difficult diplomatic relationship with Beijing, the administration can moderate the potential political fallout, analysts say. Many of the banks facilitating financing for North Korea are smaller Chinese banks. By carefully documenting how those firms are breaking U.S. money-laundering and other illicit finance laws, the administration can show China it is not going after the government, but criminal organizations, analysts said.

“Nobody’s sanctioning Bank of China , the overwhelming majority are smaller banks,” said Bruce Bechtol, a former senior Defense Intelligence Agency officer specializing in northeast Asia. “It’s not going to break the Chinese and it’s not going to ruin economic ties with the U.S.”