Germany says it is considering whether to take part in the world's largest United Nations tourism convention in Zimbabwe or stay away to protest seizures of tourism investments owned by Germans.

German ambassador Hans Gnodtke said Wednesday Zimbabwe has violated bilateral treaties on foreign investments by allowing seizures of German-owned wildlife conservancies in southeastern Zimbabwe by President Robert Mugabe's loyalists since 2011.

Gnodtke said if the European Union decided to boycott the convention, it would decrease Zimbabwe's chances of holding a successful event.

He told reporters Germany felt let down after Mugabe promised investors their interests would be safe.

Zimbabwe is set to co-host the tourism convention with neighboring Zambia in August.

Mugabe loyalists claim the invasion of private conservancies is to correct colonial-era domination of land ownership by whites.