Trade relations between Washington and Beijing are at a "difficult" stage but President Biden's administration is committed to protecting the US economy from negative impacts of China's policies, the top American trade official said Monday.

United States Trade Representative Katherine Tai said her team will "engage robustly" with China in ongoing talks over Beijing's commitments to buy American goods under a deal signed under former president Donald Trump.

"We're in a very difficult stage of this trade relationship," Tai said, adding that "the conversations are not easy."

The two countries signed a so-called "phase one" agreement in January 2020, in which Beijing pledged to increase its purchases of American products and services by at least $200 billion over 2020 and 2021.

But amid the COVID-19 pandemic, Beijing has fallen fall short of those targets.

Calling the relationship "one of the defining issues we work on," Tai said she has started the "step one" discussions with China on the trade deal but they have not yielded results as yet.

The administration's broader aim is to "defend the American economy, our workers and our businesses from the negative impacts" of China's nonmarket policies, she said in a fireside chat with the National Asian Pacific American Bar Association.

Biden recently said he is not yet ready to remove the tariffs his predecessor imposed in 2018 on Chinese products worth $370 billion, citing "unfair" trade practices.

In her comments Monday, Tai also said she is "heartened" by the prospects of reforming the World Trade Organization.

She pointed to a "universal commitment... that the WTO as an institution is important, and deserves our attention."

The Trump administration paralyzed the WTO's dispute resolution body, but Tai pledged the US would take a leadership role in the reform effort.

"We might have different visions about what we would like the WTO to be specifically, but let's engage in that process," she said.