If the Trump administration moves ahead with raising tariffs from 10% to 25% on $200 billion worth of Chinese goods, Beijing has vowed to retaliate with “necessary countermeasures.”

The threat comes as the two sides are set to begin another round of negotiations to try and salvage a trade deal between the two countries as stock markets continue to roil.

The S&P 500 had already fallen 1.0%, the Dow 0.9% and Nasdaq 1.2% by the time the market opened on Thursday after falling both Monday and Tuesday, and heading sideways on Wednesday.

After the Trump administration indicated it plans to move forward — with a new caveat — with raising the tariffs, the Chinese commerce ministry said in a statement Wednesday that escalation of the fight was neither in the best “interests” of the two countries nor the world.

“China deeply regrets it and if the U.S. tariffs are implemented, China will have to take necessary countermeasures,” Beijing said in a statement.

The new caveat was introduced Wednesday when the Trump administration said that higher tariffs would apply to products exported from China starting on Friday, and not goods that are already in transit, giving them another two weeks to a month to iron out a final deal.

China’s top trade negotiator, Liu He, is set to meet today with U.S. trade representative Robert Lighthizer and Treasury Secretary Steve Mnuchin.

Hopes were high that a trade deal would be reached soon, but the latest wrangling has sent stock markets roiling all over the world.

Hopes of course were dashed a bit when the Trump administration accused Beijing of “reneging” and trying to renegotiate parts of the deal that were reportedly settled already.

Trump said at a rally Wednesday night in Florida that China “broke the deal,” leading him to order higher tariffs.

China disputes Trump’s characterization that it reneged.

“There have been various commitments made for us,” Commerce Ministry Spokesman Gao Feng said Thursday at a press conference in Beijing. “China is credible and honors its word, and that has never changed.”

The latest round of trade talks are set to last through Friday.

In addition to China, Trump also took aim at former Vice President and 2020 candidate Joe Biden, who reportedly downplayed the threat China poses to U.S. trade, saying Beijing is “not competition for us.”

“For somebody to be so naive and say China is not a problem, if Biden actually said that, that is a very dumb statement,” Trump said on Fox News.

Kate Bedingfield, the deputy campaign manager and communications director for Biden, fired back at Trump on Twitter, saying the only people he’s gotten tough with is U.S. farmers and others who have been hurt by his tariffs.