A German military plane carrying 15 tons of military rations for survivors of Hurricane Katrina (search) was sent back by U.S. authorities, officials said Saturday.

The plane was turned away Thursday because it did not have the required authorization, a German government spokesman said.

The spokesman, speaking on customary condition of anonymity, declined to comment on a report in the German news magazine Der Spiegel that U.S. authorities refused the delivery on the grounds that the NATO military rations could carry mad cow disease.

The spokesman said U.S. authorities had since given approval for future aid flights, but it was unclear whether the German military would try again to deliver the rations.

Since Hurricane Katrina struck the United States, many international donors have complained of frustration that bureaucratic entanglements have hindered shipments to the United States.

A U.S. Embassy official, who agreed to discuss the matter only if not quoted by name, blamed the German flight's rejection on temporary technical and logistical problems that have accompanied recovery operations in the devastated region.

German military planes have flown several loads of rations to the Gulf Coast. Berlin is also sending teams equipped with high-capacity pumps to help clear floodwaters.