The next phase of a trade deal between the U.S. and China could come in stages and is yet to be determined, according to U.S. Treasury Secretary Steven Mnuchin.

Washington and Beijing announced on Friday that an agreement on phase one had been reached, pending legal procedures, an accord Mnuchin called "historic."

Phase one includes agreements on technology transfer, intellectual property, agricultural purchases, financial services access and currency conduct.

"We are going to go into a very short period of time of having the translation scrubbed, the deal will be signed in early January and then we will start on phase two," Mnuchin told CNBC's Hadley Gamble at the Doha Forum on Saturday.

"Phase two may be 2a, 2b, 2c, we'll see, but this is unto itself a huge accomplishment for the president," he added.

President Donald Trump said Friday that the U.S. would begin negotiations on the next phase of the trade deal "immediately, rather than waiting until after the 2020 Election."

The first phase will see the U.S. delay additional 15% tariffs on $160 billion worth of Chinese imports and to refrain from imposing new duties for as long as negotiations continue amicably, while Beijing has agreed to significantly increase American agricultural purchases.

In tweets, Trump said the White House would leave 25% tariffs on $250 billion in imports in place while cutting existing duties on another $120 billion in products to 7.5%.

Global markets rallied on Friday in reaction to the news, having been largely beholden to the bruising trade war between the world's two-largest economies over the past 18 months.