"Checks are underway, there is no need to start speculating in a way that could cause alarm," Interior Minister Angelino Alfano said on Canale5 television.
"It is too early to say if it was a case of a violation of immigration and citizenship rules or anything more than that. We will know more in the coming hours."
Flight EZY4917 from Rome's Fiumicino airport to London-Luton was within minutes of its scheduled 12:35 p.M (1135 GMT) take-off yesterday when Italian border agents boarded the plane and removed the man, easyJet confirmed.
"We don't know it was definitely a fake passport. That is under police investigation," the spokesman said.
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After all bags were removed from the hold and rechecked, the plane took off later in the afternoon. EasyJet said five passengers unconnected with the suspect opted not to fly in the immediate aftermath of the incident and were switched to later flights.
The other eight expelled were five Tunisians, an Egyptian, a Moroccan and a Turk.