Treasury Secretary Steven Mnuchin said the U.S. and China are making progress on a trade deal, including resolving a key sticking point that's been dragging out the process.

"We've pretty much agreed on an enforcement mechanism. We've agreed that both sides will establish enforcement offices that will deal with the ongoing matters. This is something both sides are taking very seriously," Mnuchin told Sara Eisen on CNBC's The Exchange on Wednesday. "We are really focused on the execution of the documents."

Mnuchin declined to comment on whether the U.S. will use tariffs as an enforcement tool. President Donald Trump has previously said his administration's tariffs on $250 billion in Chinese goods could stay in place even after the two countries strike a deal. China has pushed for the removal of duties as part of an agreement.

The secretary revealed that the meeting with Chinese Vice Premier Liu He on Tuesday was "productive."

"We went into late last night, and we have another call scheduled for tomorrow morning ... we still have some important issues to address, but both sides are working very hard on this agreement," Mnuchin said.

U.S. Trade Representative Robert Lighthizer and Mnuchin are negotiating with Chinese representatives to work up a long-term trade deal with China. The world's two largest economies have imposed tariffs on hundreds of billions of dollars of goods. Trump said last week that a trade deal may be reached in four weeks, but Munchin said there isn't a specific timeline.

"We are hopeful we can do this quickly, but we are not going to set an arbitrary deadline," Mnuchin said. "If we can complete this agreement, this will be the most significant changes to the economic relationship between the U.S. and China in really the last 40 years. The opening of the Chinese economy will be a tremendous opportunity with structural changes that will benefit U.S. workers and U.S. companies."