The head of the World Health Organization called for further investigation into whether the novel coronavirus first leaked from a laboratory, in remarks to the press on Tuesday.

WHO director-general Dr. Tedros Adhanom Ghebreyesus said that “all hypotheses remain on the table” regarding the origin of the coronavirus. Dr. Tedros made his remarks during the unveiling of a WHO report on the origin of the pandemic, which concludes that a lab leak is “highly unlikely.”

“Although the team has concluded that a laboratory leak is the least likely hypothesis, this requires further investigation, potentially with additional missions involving specialist experts, which I am ready to deploy,” Dr. Tedros said.