U.S. stock futures fell in pre-market trading Monday after President Trump's chief economic adviser said he expected China to retaliate against the higher tariffs that the United States imposed last week. It is another sign the trade war between the two countries is escalating.

Contracts on the Dow Jones industrial average fell 344 points, or 1.3%, in pre-market trading on Monday, while the Standard & Poor’s 500 futures slid 42 points, or 1.5%.

“The expected countermeasures have not yet materialized. We may know more today or even this evening or tomorrow,” Larry Kudlow said on “Fox News Sunday.” He also said that the president’s plan to increase U.S. tariffs on more Chinese imports could take months to implement.

President Trump tried to increase pressure on China in a series of tweets early Monday, saying that the country would be "hurt very badly" if it didn't make a trade deal with the United States.

On Friday, the U.S. raised duties on $200 billion of Chinese goods to 25% from 10% after the White House said that Beijing had backpedaled on earlier trade proposals. President Donald Trump also said Friday that the “process has begun” to hike tariffs on another $325 billion in Chinese imports.

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Trade negotiations between the two countries ended without a deal on Friday, although Treasury Secretary Steven Mnuchin said the talks were “constructive.” President Trump later tweeted that the discussions were "candid and constructive."

China’s Commerce Ministry on Thursday said the country would retaliate by imposing "necessary countermeasures" if higher tariffs went into effect on Friday. So far, though, China has made no moves.

“I think that China felt they were being beaten so badly in the recent negotiation that they may as well wait around for the next election, 2020, to see if they could get lucky & have a Democrat win,” Trump tweeted Saturday.