But Bo Redeborn, an official of the European air traffic agency, said later that the F-16 belonged to the Belgian Air Force. The incident highlighted the danger of flying through the ash clouds that have paralyzed civilian air traffic over much of Europe over the last five days.
Volcanic ash tends to stick to a jet engine's interior parts, such as the turbines, where it melts to form a glassy coating that restricts air flow. It also can clog the tiny cooling holes on the jet's fan blades, leading to overheating and eventual engine failure.
NATO Secretary-General Anders Fogh Rasmussen said on Monday that the ash cloud was not affecting the alliance's military readiness, although he declined to comment on specific missions.
"I can assure you that Icelandic volcano does not have any effect on our operations, nor our territorial defense of the allied member states," he said.
Addressing reports that some troop flights across Russia and Central Asia to Afghanistan had to be delayed due to the closures of air space and other air traffic restrictions, he stressed that operations in Afghanistan had not been affected.
"Our air forces will always take necessary steps to ensure they are capable to conduct their operations," Fogh Rasmussen said.
NATO officials said two of the alliance's Boeing E-3A early warning planes were moved on Thursday from their base in Germany to an airfield in Italy, and were conducting regular patrols from there.