WASHINGTON—The Trump administration imposed sanctions against a key Chinese military-research unit for two Russian arms deals, widening the scope of targets as it launches a new phase of Washington’s escalating sanctions campaign against Moscow.

The U.S. Treasury and State Departments, using a new sanctions power mandated by Congress last year to target Moscow’s intelligence operations and defense industry, sanctioned China’s Equipment Development Department for the recent purchases of Sukhoi Su-25 jet fighters and S-400 surface-to-air missiles from Russia.

The sanctions, which prohibit financial and business ties to the Chinese entity, are meant to send a message to other countries considering similar Russia arms deals, potentially curbing an important revenue stream for Moscow and important a tool in the Kremlin’s diplomatic kit, U.S. officials said.

And while the officials said the sanctions weren’t intended to undermine other countries’ defense capabilities, Washington’s first use of the new power targets a strategic unit of the Chinese military. Li Shangfu, who was also sanctioned as the unit’s director, previously oversaw cyber, space and other high-tech warfare for China’s army.

In related actions, the State Department also added 33 Russian intelligence and defense agents to its blacklist of security companies and officials, and the White House rolled out an executive order that details the penalties it plans to apply in the new phase of its pressure campaign. Among those added to the State Department’s blacklist are Russian individuals and companies indicted earlier this year by federal prosecutors for their role in U.S. election interference and firms involved in supporting Moscow’s military operations in Syria and Ukraine.