WHO director-general Tedros Adhanom Ghebreyesus presented the plan to member states a day after saying that investigations were being hampered by the lack of raw data on the first days of spread of COVID-19 in China.
Phase two work would require studies of humans, wildlife and animal markets in Wuhan, including Huanan wholesale market, he said in remarks released by the agency.
It would also require "audits of relevant laboratories and research institutions operating in the area of the initial human cases identified in December 2019", Tedros said.
Diplomats said that China, which has resisted a return by international scientists, voiced objections at the closed-door talks saying: "This plan is not a basis for future studies."
A WHO-led team spent four weeks in and around the central city of Wuhan with Chinese researchers and said in a joint report in March that the virus had probably been transmitted from bats to humans through another animal.
But countries including the United States and some scientists have demanded further investigation, particularly into the Wuhan Institute of Virology which was conducting research into bats.
"Finding the origins of this virus is a scientific exercise that must be kept free from politics. For that to happen, we expect China to support this next phase of the scientific process by sharing all relevant data in a spirit of transparency," Tedros said.
China has called the theory that the virus may have escaped from a Wuhan laboratory "absurd" and said repeatedly that "politicizing" the issue would hamper investigations.
At a regular news briefing on Friday, when asked about Tedros's earlier comments on the need for more data from China, China's foreign ministry spokesperson Zhao Lijian said that some data was unable to be copied or leave China as it involved personal information.
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