On January 21, Xi reportedly asked Tedros not to announce that the virus could be transmitted between humans and to delay any declaration of a pandemic, the German intelligence agency BND found.
"Der Spiegel reports of a January 21, 2020, telephone conversation between Director-General Tedros Adhanom Ghebreyesus and President Xi Jingping of China are unfounded and untrue," said the WHO in a statement on Saturday. "Dr Tedros and President Xi did not speak on Jan. 21, and they have never spoken by phone. Such inaccurate reports distract and detract from WHO's and the world's efforts to end the COVID-19 pandemic."
The WHO noted that China confirmed human-to-human transmission on January 20, a day before the purported conversation between Jingping and Ghebreyesus
The BND concluded that the delay caused the world to waste four to six weeks it could have used better preparing to fight the outbreak. The WHO did not end up declaring the virus an international emergency until the end of January.
Germany's Robert Koch Institute also said that it had to turn for the BND for information about the virus at first, because China originally failed to reveal all the relevant information about the virus.
The WHO declared that the coronavirus outbreak could be officially classified as a pandemic in mid-March.
A team of scientists led by the University of Cambridge found that the virus may have been spreading since September, placing the initial outbreak somewhere between September 13 and December 7, according to the South China Morning Post.
The team analyzed a large number of strains from around the world using a phylogenetic network - a mathematical algorithm used to map the global movement of organisms based on the mutation of their genes. The study has not yet been peer-reviewed.
"If I am pressed for an answer, I would say the original spread started more likely in southern China than in Wuhan," said University of Cambridge geneticist Peter Forster, according to SCMP. "But proof can only come from analyzing more bats, possibly other potential host animals, and preserved tissue samples in Chinese hospitals stored between September and December."
A study conducted by scientists at University College London's Genetics Institute found that the virus probably began spreading in humans "sometime around Oct. 6, 2019 to Dec. 11, 2019."
US President Donald Trump instructed his administration to temporarily halt funding to the WHO in April over the organizational response regarding the coronavirus pandemic.
Both Trump and Secretary of State Mike Pompeo have claimed that there is evidence that the coronavirus emerged from a Chinese laboratory, despite statements by health professionals and intelligence agencies to the contrary.
Zach Keyser and Reuters contributed to this report.