Hackers working for the Iranian government have attempted to break into the personal email accounts of staff at the World Health Organisation during the coronavirus outbreak.
It is not clear if any accounts were compromised, but the attacks show how the WHO and other organisations at the centre of the global effort to contain the coronavirus have come under a sustained digital bombardment by hackers seeking information.
Reuters reported in March that hacking attempts against the United Nations health agency and its partners had more than doubled since the beginning of the coronavirus crisis, which has killed more than 40,000 worldwide.
The latest effort has been ongoing since March 2 and attempted to steal passwords from WHO staff by sending malicious messages designed to mimic Google web services to their accounts, a common hacking technique known as "phishing", according to four people briefed on the attacks.
Reuters confirmed their findings by reviewing a string of malicious websites and other forensic data.
"We've seen some targeting by what looks like Iranian government-backed attackers targeting international health organisations generally via phishing," said one of the sources, who works for a large technology company that monitors internet traffic for malicious cyber activity.
WHO spokesman Tarik Jasarevic confirmed personal email accounts of staff were being targeted but said it did not know who was responsible.
"To the best of our knowledge, none of these hacking attempts was successful," he said.
Iran's government denied any involvement. "These are all sheer lies to put more pressure on Iran," said a spokesman at the information technology ministry. "Iran has been a victim of hacking."
Karim Hijazi, chief executive of cyber intelligence firm Prevailion, shared his recently captured data with Reuters that shows a sophisticated hacking group was actively targeting WHO.
Mr Hijazi said the hackers' identity was difficult to determine, although their techniques appeared advanced.
Iran has suffered enormous loss of life from the coronavirus, and infections have reached the inner circle of the country's leadership.