Reported by BBC World
Watch: Sniffer dog inspects Ryanair plane in Spain after suspected bomb threat
Seven passenger planes across Europe, two of which departed from the UK, have been inspected following a series of suspected bomb threats.
Two Ryanair flights, one originating from Dublin and the other from Lisbon, were searched after landing in Rome following anonymous tips but no explosives were found, sources at the city's Fiumicino airport told the BBC.
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The Dublin flight was escorted by the Italian Air Force until landing. Authorities have also searched planes in Poland, Spain and Bulgaria.
While officially there is no link between them, authorities from various countries will be co-operating to assess whether this was a co-ordinated attack, designed to disrupt airspace.
The UK government described today's incidents as "malicious hoax threats".
In a statement it said it had "one of the most robust aviation security systems in the world, with well-tested processes for dealing with any potential threats, as well as malicious hoax threats, like those we've seen today".
Aviation security expert Paul Mason said bomb threats on passenger planes "don't happen that frequently", which made the latest incidents "unusual".
"It sounds like they've been made in a credible manner across a broad range of airlines," Mason told BBC Radio 5 Live. "That would suggest to me that it's been a very deliberate act by a typical actor rather than a load of coincidental, malicious calls."
He said "there are a lot of processes" that the onboard crew and people on the ground must go through "to validate the credibility of the threat".
A flight may be asked to divert if the credibility of a threat "is of a certain level", Mason added, and in some cases the onboard crew may not even be advised on what the ground operators were dealing with.
Two of the four flights were en route to Warsaw Chopin airport
In Rome, sources at Fiumicino airport told the BBC police bomb disposal experts carried out standard security protocols to ensure the safety of all passengers and crew.
Inspections of the passengers, luggage, and the aircraft yielded negative results,…