President Donald Trump on Saturday openly challenged reporting of coronavirus statistics in China and Iran as the U.S. death toll climbed to 38,000 – almost doubling over the prior seven days.

Iran claims to have recorded 5,000 deaths and China reports fewer than 4,700, even after Beijing acknowledged this week it had underreported cases in the region around Wuhan, the origin of the global spread of the virus, which causes a disease known as COVID-19.

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"Does anybody really believe this number?" Trump repeatedly asked reporters, interrupting a presentation from immunologist and White House coronavirus response coordinator Deborah Birx as she referenced a slide on mortality rates in countries around the world.

Birx, whose presentations are ordinarily heavy on statistics about the virus and its effects, more subtly questioned the figures, describing China's numbers as "basically unrealistic." She stressed the need for countries to report accurately how a new disease has affected their populations, particularly those countries that were among the first to experience it.

"This is why the reporting is so important," she said.

Trump has repeatedly criticized China for not doing more to stem the spread of the virus, despite praising Beijing in late January for its initial response.

During Saturday's briefing – in which the president veered into unrelated topics like the Russia investigation, the Obama administration's Iran policy and Joe Biden's record – Trump declined to say whether China is currently cooperating with the U.S., noting that both countries are investigating the source of the outbreak.

"They said they're doing an investigation," Trump said during a press briefing at the White House. "So let's see what happens with their investigation. We're doing an investigation, also."

Trump later said China should face repercussions if it was revealed to be responsible for the global spread of the virus, adding, "If it was a mistake, a mistake is a mistake. But if they were knowingly responsible, then there should be consequences."

The U.S. was poised to end Saturday with more than 27,000 new cases of coronavirus and almost 1,200 deaths, a decrease from surges in both cases and deaths on Thursday and Friday.

The state of New York, the epicenter of the virus' spread and still the greatest source of cases and deaths, saw more than 25 percent decreases in both as of Saturday evening. New York Gov. Andrew Cuomo warned against complacency despite the positive trend, noting that more than 500 New Yorkers had died as of Saturday morning, and 2,000 more infected people entered overburdened hospitals.

Other states saw dramatic increases in fatal cases, including Massachusetts where the death toll increased by 100 percent to 137 on Friday, and in Michigan where the deaths on Friday increased more than 200 percent to 231. Birx noted that the numbers had shifted this week due to states including probable cases in their death tolls, even though they could have occurred as long ago as March.