The head of the World Health Organization said Saturday that he was "rethinking" his decision to name Zimbabwe's President Robert Mugabe a goodwill ambassador, as global outrage over the move mounted.

Tedros Adhanom Ghebreyesus, the director-general of the UN health agency, had this week asked Zimbabwe's 93-year-old authoritarian leader to serve in the role to help tackle non-communicable diseases like heart attacks, strokes and asthma across Africa.

The decision triggered confusion and anger among key WHO member states and activists who noted that Zimbabwe's health care system, like many of its public services, has collapsed under Mugabe's regime.

"I'm listening. I hear your concerns. Rethinking the approach in light of WHO values. I will issue a statement as soon as possible," Tedros, a former Ethiopian health minister, said on Twitter.

Tedros took charge of WHO in July, becoming the first African to lead the powerful UN agency.

The US said Zimbabwean President Robert Mugabe's appointment as a WHO goodwill ambassador contradicts United Nations ideals. Photo: AFP

In announcing the appointment in Uruguay's capital this week, Tedros had praised Zimbabwe as "a country that places universal health coverage and health promotion at the centre of its policies to provide health care to all."

'Bad April Fool's joke'

Britain, Canada and the US on Saturday joined the widening chorus of critics of the decision.

"This appointment clearly contradicts the United Nations ideals of respect for human rights and human dignity," the US State Department said.

Britain said the move was "surprising and disappointing, particularly in light of the current US and EU sanctions against him."

"We have registered our concerns with WHO Director-General Dr Tedros Adhanom Ghebreyesus," a foreign office statement read.

And Canadian Prime Minister Justin Trudeau termed the appointment "absolutely unacceptable," and said he "quite frankly... thought it was a bad April Fool's joke."

Zimbabwean activist and human rights lawyer Doug Coltart said on Twitter that a "man who flies to Singapore for treatment because he has destroyed Zimbabwe's health sector is WHO's goodwill ambassador."

Mugabe, who has been in power since 1980, is in increasingly fragile health and makes regular trips abroad for medical treatment.

"Mugabe doesn't trust Zimbabwe health care he destroyed (he travels abroad) but @WHO's Tedros names him ambassador," the head of Human Rights Watch, Ken Roth, added in a tweet.

'Sickening'

UN Watch, a group primarily known for defending Israel at the world body, called the decision "sickening."

"Amid reports of ongoing human rights abuses, the tyrant of Zimbabwe is the last person who should be legitimized by a UN position of any kind," the group's executive director Hillel Neuer said in a statement.

WHO had earlier on Saturday pointed to Zimbabwe's record on tobacco, NCDs and Tedro's desire to engage senior politicians as justifications for the Mugabe honour.

"Dr Tedros has frequently talked of his determination to build a global movement to promote high-level political leadership for health," spokesman Christian Lindmeier said in an email.

"Zimbabwe has ratified the WHO FCTC (Framework Convention on Tobacco Control) in 2014 and the government has launched a levy fund for NCDs to generate revenues for health promotion, including NCD prevention and control."

UN agencies often name high-profile personalities as goodwill ambassadors to draw attention to their work, including actress Angelina Jolie with the refugee agency UNHCR.