U.S. officials believe China covered up the extent of the coronavirus outbreak — and how contagious the disease is — to stock up on medical supplies needed to respond to it, intelligence documents show.

Chinese leaders “intentionally concealed the severity” of the pandemic from the world in early January, according to a four-page Department of Homeland Security intelligence report dated May 1 and obtained by The Associated Press. The revelation comes as the Trump administration has intensified its criticism of China, with Secretary of State Mike Pompeo saying Sunday that that country was responsible for the spread of disease and must be held accountable.

The sharper rhetoric coincides with administration critics saying the government’s response to the virus was slow and inadequate. President Donald Trump’s political opponents have accused him of lashing out at China, a geopolitical foe but critical U.S. trade partner, in an attempt to deflect criticism at home.

Not classified but marked “for official use only,” the DHS analysis states that, while downplaying the severity of the coronavirus, China increased imports and decreased exports of medical supplies. It attempted to cover up doing so by “denying there were export restrictions and obfuscating and delaying provision of its trade data,” the analysis states.

The report also says China held off informing the World Health Organization that the coronavirus “was a contagion” for much of January so it could order medical supplies from abroad — and that its imports of face masks and surgical gowns and gloves increased sharply.

Those conclusions are based on the 95% probability that China’s changes in imports and export behavior were not within normal range, according to the report.

China informed the WHO of the outbreak on Dec. 31. It contacted the U.S. Centers for Disease Control on Jan. 3 and publicly identified the pathogen as a novel coronavirus on Jan. 8.

Chinese officials muffled doctors who warned about the virus early on and repeatedly downplayed the threat of the outbreak. However, many of the Chinese government’s missteps appear to have been due to bureaucratic hurdles, tight controls on information, and officials hesitant to report bad news. There is no public evidence to suggest it was an intentional plot to buy up the world’s medical supplies.

In a tweet on Sunday, the president appeared to blame U.S. intelligence officials for not making clearer sooner just how dangerous a potential coronavirus outbreak could be. Trump has been defensive over whether he failed to act after receiving early warnings from intelligence officials and others about the coronavirus and its potential impact.

“Intelligence has just reported to me that I was correct, and that they did NOT bring up the CoronaVirus subject matter until late into January, just prior to my banning China from the U.S.,” Trump wrote without citing specifics. “Also, they only spoke of the Virus in a very non-threatening, or matter of fact, manner.”

Trump had previously speculated that China may have unleashed the coronavirus due to some kind of horrible “mistake.” His intelligence agencies say they are still examining a notion put forward by the president and aides that the pandemic may have resulted from an accident at a Chinese lab.

Speaking Sunday on ABC’s “This Week,” Pompeo said he had no reason to believe that the virus was deliberately spread. But he added, “Remember, China has a history of infecting the world, and they have a history of running substandard laboratories.”

“These are not the first times that we’ve had a world exposed to viruses as a result of failures in a Chinese lab,” Pompeo said. “And so, while the intelligence community continues to do its work, they should continue to do that, and verify so that we are certain, I can tell you that there is a significant amount of evidence that this came from that laboratory in Wuhan.”

The secretary of state appeared to be referring to previous outbreaks of respiratory viruses, like SARS, which started in China. His remark may be seen as offensive in China. Still, Pompeo repeated the same assertion hours later, via a tweet Sunday afternoon.

Experts say the virus arose naturally in bats, and make it clear that they believe it wasn’t man-made. Many virologists say the chance that the outbreak was caused by a lab accident is very low, though scientists are still working to determine a point at which it may have jumped from animals to humans.

Beijing has repeatedly pushed back on U.S. accusations that the outbreak was China’s fault, pointing to many missteps made by American officials in their own fight against the outbreak. China’s public announcement on Jan. 20 that the virus was transmissible from person to person left the U.S. nearly two months to prepare for the pandemic, during which the U.S. government failed to bolster medical supplies and deployed flawed testing kits.

“The U.S. government has ignored the facts, diverted public attention and engaged in buck-passing in an attempt to shirk its responsibility for incompetence in the fight against the epidemic,” Chinese Ministry of Foreign Affairs spokesman Geng Shuang said Friday.