Mrs Mugabe is alleged to have overseen the export of large consignments of ivory to several destinations around the world, including China, the United Arab Emirates and the US.

The Herald reports, quoting a source, that officers have questioned officials from the country's Parks and Wildlife Management Authority.

Mrs Mugabe is alleged to have acquired export permits under the pretext that she was sending the ivory to leaders of various countries as “gifts”, the report says.

The beleaguered former first lady has not commented on the allegations.

She has been targeted after her husband - the former Zimbabwe leader Robert Mugabe - was forced out of office following a military takeover in November.

Her farm was invaded last week by illegal miners looking for gold.