WASHINGTON (Reuters) – U.S. President Donald Trump on Monday slammed China over its trade practices, saying the United States was losing billions to Beijing and vowing to protect American commerce as tension escalated following his weekend threat to hike tariffs.

On Sunday, Trump said he would ratchet up tariffs on $200 billion worth of imports from China, escalating the dispute marked by tit-for-tat duties between Washington and Beijing as ongoing talks were set to continue this week.

Global stock markets tumbled on Monday. Chinese shares fell 6 percent, U.S. stock market futures tumbled 1.6 percent and European stocks slid to a one-month low.

Trump appeared to defend his Sunday statement, citing the trade deficit between the United States and China. “Sorry, we’re not going to be doing that anymore!” he tweeted early Monday.

Trump and his advisers had said the talks were progressing well amid a round of negotiations in Beijing last week. But on Sunday, Trump said a trade deal was coming together too slowly.

He also said he would impose tariffs of 25 percent on $325 billion of Chinese goods “shortly,” which would essentially mean all goods imported from China into the United States would be blanketed by duties.

Trump said later Monday he had discussed trade and North Korea with Japanese Prime Minister Shinzo Abe, but provided no additional details.

Abe told reporters the two countries would “respond together” to North Korea “going forward.” North Korea fired several “unidentified short-range projectiles” off of its coast on Saturday.