HONG KONG (AP) Hong Kongs oldest zoo is seeking answers in a monkey medical mystery after nine animals died in two days, including three members of a critically endangered species.

Part of the Hong Kong Zoological and Botanical Gardens has been sealed off and disinfected, and experts have been called in to conduct necropsies and toxicological tests, Hong Kong leader John Lee said in his weekly press briefing Tuesday.

Eight monkeys were found dead on Sunday, and another died Monday after unusual behavior.

The deceased animals included a De Brazzas monkey, a common squirrel monkey, four white-faced sakis and three cotton-top tamarins a species listed as critically endangered by the International Union for Conservation of Nature.

Whenever we have any news, if theres a new development, an announcement should be made as soon as possible, so that everyone can know about the facts, Lee said.