The U.S. and a coalition of 37 other countries imposed unprecedented export controls on Russia over the past year in response to its unprovoked assault on Ukraine, and more actions are in the works.

Alan Estevez, Under Secretary of Commerce for Industry and Security, said Russia is working hard to evade those controls, but that the goods that are being smuggled in cannot replace everything that needs to be resupplied.

"Evasion techniques are not going to get you the scale you need to reconstitute your military over time," Estevez said in an interview with Reuters.

Estevez's comments come amid reports of new ways of getting tech to Russia.

Estevez, whose agency oversees U.S. export restrictions, noted that Russia's chip imports have dropped by nearly 70 percent, and that bigger items are even harder to get through.

"It's easier to smuggle micro-electronics than it is to smuggle a CNC machine," Estevez said, referring to a computer-coded machine used for high-precision metal shaping and milling.

Estevez reiterated that export controls and financial sanctions on Russia work over time, not at once.

"It's not a guillotine," he said.

With the one-year anniversary of the war next week, he said that evasion and diversion of U.S. technology to Russia are top of mind, because over time underground networks become more sophisticated.

Estevez said China generally appears to be complying with U.S. restrictions on sending American-origin technology to Russia, and that while some Chinese companies had been supplying Russia, he had no evidence China's top chipmaker SMIC is doing so.

"Over time, Putin's war machine is going to be crippled, and as we continue to supply arms to Ukraine, their military capability is going up and Putin's is going down," he said.