Glenn Thomas, a former BBC journalist working as a media officer for the Geneva-based World Health Organization, is among the 298 who died aboard Malaysian Airlines Flight MH17.
Thomas, 49 and a British national, was one of 100 people on the plane en route to Australia for a global AIDS conference in Melbourne.
"For the time being we would like to give his family time to grieve," a WHO spokesman said. "We have lost a wonderful person and a great professional. Our hearts are broken. We are all in shock."
The United Nations in Geneva held a minute of silence in tribute to Thomas.
The BBC reported that Thomas lived in Scotland and was one of nine UK residents aboard the flight. "He was a much loved and respected colleague and the BBC World News team are reeling from this very sad news about their friend," said BBC World News controller Richard Porter.
Friends and former colleagues of Thomas are posting messages on Twitter with the hashtag #RIPGlennWHO.
Thomas was with WHO for 11 years, according to his LinkedIn profile, after five-plus years as a producer with the BBC.