Treasury Secretary Steven Mnuchin expressed optimism Monday that the U.S. and China have a workable first-phase agreement that addresses some key elements of the trade war between the two nations.

"We made substantial progress last week in the negotiations," Mnuchin said during an interview with CNBC's "Squawk Box." "We have a fundamental agreement that is subject to documentation."

Among the key points he said that were addressed during the most recent round of talks were intellectual property rights, financial services including currency and foreign exchange, and "very significant structural issues" dealing with agriculture, a key sticking point in the tit-for-tat tariff battle.

In light of the tentative accord, President Donald Trump has said he will postpone tariffs on the remaining $300 billion worth of Chinese goods not already subject to duties. They had been due to begin Tuesday. Mnuchin said, though, that those tariffs will be implemented if China does not sign off on the current deal.

China is indicating that it wants another round of talks before it agrees to the phase-one terms, according to reporting by CNBC's Kayla Tausche.

Still, Mnuchin said the talks resulted in a "great deal for our farmers" that will result in purchases in a $40 billion to $50 billion range.

"China has agreed on agriculture that they're going to take off tariffs on agriculture and they're going to start purchasing agriculture," he said. "They had been in the market, but they'll be stepping that up."

Markets have been highly sensitive to news coming out of the trade war. Wall Street was looking at a slightly negative open Monday despite the apparently optimism over the talks.