U.S. President Donald Trump waves as he departs from the White House on July 12, 2017 in Washington, DC.

It's unfortunate that President Donald Trump has chosen to add fuel to an already heated spat with China just as officials from both countries have signaled their willingness to negotiate to avoid escalating trade tensions, said a former deputy U.S. trade representative.

"The timing is especially unfortunate," Miriam Sapiro, a former deputy and acting U.S. trade representative during the Obama administration, told CNBC's "Squawk Box" on Friday.

"(The latest development) just makes it more difficult for the Chinese government to engage. Either China matches this escalation, plays tit-for-tat, or it takes a high road and score significant leadership point," she added.

Trump on Thursday proposed $100 billion in additional tariffs on Chinese products. The president said that's a response to China's "unfair retaliation" against an up to $60 billion of tariffs that the U.S. had earlier announced.

Given that China previously said "it is only polite to reciprocate," Sapiro said it's unlikely that the Asian economic giant would back off.

That would heighten the prospect of a trade war between the two largest economies in the world, which would then hurt the "very U.S. companies that the White House has been trying to help," noted Sapiro, who's now managing director of Sard Verbinnen & Co's New York office.