The U.S. will impose an additional 10 percent tariff on $300 billion in Chinese imports, starting next month, President Donald Trump announced Thursday via tweet.

Wall Street immediately pulled back on the news, with the Dow Jones Industrial Average falling from a 300-point gain to a decline of 100 points.

U.S. Trade Representative Robert Lighthizer and Treasury Secretary Steven Mnuchin just returned from trade talks in Shanghai, where little progress appeared to have been made. A new meeting had been set up for September, the White House said earlier this week.

“We thought we had a deal with China three months ago, but sadly, China decided to re-negotiate the deal prior to signing,” wrote Trump in a series of tweets Thursday afternoon.

“More recently, China agreed to buy agricultural product from the U.S. in large quantities, but did not do so. Additionally, my friend President Xi said that he would stop the sale of Fentanyl to the United States – this never happened, and many Americans continue to die!” Trump tweeted.

“Trade talks are continuing, and during the talks the U.S. will start, on September 1st, putting a small additional Tariff of 10% on the remaining 300 Billion Dollars of goods and products coming from China into our Country. This does not include the 250 Billion Dollars already Tariffed at 25%… We look forward to continuing our positive dialogue with China on a comprehensive Trade Deal, and feel that the future between our two countries will be a very bright one!”