The Biden White House expressed additional concerns Thursday that China is withholding information that would either prove or disprove claims that the coronavirus pandemic originated at the Wuhan Institute of Virology.

Press secretary Jen Psaki, responding to a question from Fox News’s Peter Doocy, declined to say whether the administration had seen any circumstantial evidence that would disprove the lab leak theory, adding that “disproving a negative” is not a “responsible approach” toward investigating the “root causes of a pandemic that has killed hundreds of thousands of people in the United States.”