GENEVA (AP) — One of the leading critics of the World Health Organization says he was recently invited to sit on the U.N. health agency's Zika emergency committee — only to have his invitation rescinded when he refused to sign a confidentiality clause.

Last month, Canadian professor Amir Attaran and colleagues wrote an open letter to WHO, accusing it of shirking its responsibilities by not considering whether to recommend delaying or canceling the Rio de Janeiro Olympics. He then received an invitation to sit on WHO's independent committee of Zika experts, which meets Tuesday.

WHO sent Attaran a confidentiality agreement, seeking his promise that he would not reveal details of committee deliberations, which he refused to sign.