U.S. intelligence agencies remain divided on the origins of the coronavirus but believe China’s leaders did not know about the virus before the start of the global pandemic, according to results released Friday of a review ordered by President Joe Biden.

According to an unclassified summary, four members of the U.S. intelligence community say with low confidence that the virus was initially transmitted from an animal to a human. A fifth intelligence agency believes with moderate confidence that the first human infection was linked to a lab. Analysts do not believe the virus was developed as a bioweapon and most agencies believe the virus was not genetically engineered.

The Office of the Director of National Intelligence said in a statement Friday that China “continues to hinder the global investigation, resist sharing information and blame other countries, including the United States.” Reaching a conclusion about what caused the virus likely requires China’s cooperation, the office said.

The cause of the coronavirus remains an urgent public health and security concern worldwide. In the U.S., many conservatives have accused Chinese scientists of developing COVID-19 in a lab and allowing it to leak. State Department officials under former President Donald Trump published a fact sheet noting research into coronaviruses conducted at the Wuhan Institute of Virology, located in the Chinese city where the first major known outbreak occurred.

The scientific consensus remains that the virus most likely migrated from animals in what’s known as a zoonotic transmission. So-called “spillover events” occur in nature, and there are at least two coronaviruses that evolved in bats and caused human epidemics, SARS1 and MERS.

In a statement, Biden said China had obstructed efforts to investigate the virus “from the beginning.”

“The world deserves answers, and I will not rest until we get them,” he said. “Responsible nations do not shirk these kinds of responsibilities to the rest of the world.”

China’s embassy in Washington hit back with a lengthy statement saying the U.S. had “fabricated” the report and invoking mistaken American intelligence about weapons of mass destruction prior to the Iraq War.

“The report by the intelligence community is based on presumption of guilt on the part of China, and it is only for scapegoating China,” the embassy said. “Such a practice will only disturb and sabotage international cooperation on origin-tracing and on fighting the pandemic, and has been widely opposed by the international community.”

Biden in May ordered a 90-day review of what the White House said was an initial finding leading to “two likely scenarios”: an animal-to-human transmission or a lab leak. The White House said then that two agencies in the 18-member intelligence community leaned toward the hypothesis of a transmission in nature and another agency leaned toward a lab leak.

The Office of the Director of National Intelligence on Friday did not identify which agencies supported either hypothesis. But it noted some of the same hurdles facing the World Health Organization and scientists worldwide: a lack of clinical samples and data from the earliest cases of COVID-19.

In conducting the review, intelligence agencies consulted with allied nations and experts outside of government. An epidemiologist was brought into the National Intelligence Council, a group of senior experts that consults the head of the intelligence community.