Lisbon - The Portuguese airforce has been on alert since late on Tuesday, when several authorities and witnesses reported seeing a luminous unidentified flying object, the national press reported.
"Military radar surveillance has been increased and F16 planes are ready for take-off," reported the tabloid daily, Correio da Manha, on Thursday.
It said the Portuguese civil protection service had received scores of calls from people who reported briefly seeing a silent, luminous object in the sky on Tuesday night, giving off white smoke.
Colonel Carlos Barbosa of the air force confirmed to Lusa news agency that military radars had detected "a target... that was not identified as a plane" for two or three minutes.
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