Germany's Der Spiegel magazine said the shipment was due in Germany on 20 March but never arrived after disappearing at the end of last week.

It is unclear why the masks were in Kenya.

“The authorities are trying to find out what happened,” a German defence ministry spokeswoman told the Reuters news agency.

Another government source is quoted as saying: “Whether this [is] a matter of theft or a provider who isn’t serious, is being cleared up by customs.”

According to Reuters, Kenya’s health ministry declined to comment and a Kenya Airports Authority (KAA) spokeswoman said the situation was being assessed.