BERLIN — Officials across Europe reported more bomb threats against multiple flights on Friday, following a string of hoaxes that have caused flight diversions this week.

No suspicious items were found and no one was injured, but the threats have raised concern because they came as Europe digests a slew of other recent disruptions — including attacks on supermarket refrigeration systems and drone incursions.

French Prime Minister Sebastien Lecornu’s office said Friday that “four new bomb threats were made today against aircraft flying over French territory.” The planes landed safely and bomb disposal experts were conducting inspections. The statement didn’t give further details on the flights affected.

A flight from Prague to Bucharest operated by Romanian carrier Tarom received a bomb threat. The plane landed at its intended destination, and airport administration officials said the bomb threat proved to be false.

Portuguese police said they were informed of a bomb threat targeting a Ryanair flight traveling from Lisbon to Rome, and carried out a security inspection once the aircraft landed in Lisbon. Passengers and luggage scheduled to travel to Rome underwent additional security screening before boarding.

Police in Venice said a WizzAir flight from Prague to Rome was diverted to the Italian city after a bomb alert. Passengers were evacuated after the aircraft landed, and authorities were carrying out security checks. The inspections had so far produced negative results, according to police. Air traffic at the airport was temporarily suspended but resumed.

Meanwhile, police in Denmark and the Czech Republic both said they investigated threats to air traffic.

In the Danish capital, Copenhagen, police said Friday they went to the airport for a second consecutive day “in connection with threats directed at air traffic” as a precautionary measure. They said they assessed that there had been no danger to passengers or to others at the airport, and that air traffic was proceeding safely and without disruption.

Czech police also said they were again dealing with threats against arriving and departing planes on Friday. They said necessary security measures were taken in cooperation with Prague’s Vaclav Havel Airport that had “a minimal impact on the normal operations at the airport.”

More than two dozen flights were affected by threats earlier in the week, with some diverted as authorities scrambled to rule out any danger.

Fake bomb threats are relatively common but it is unusual to see so many in such a short period.

It remains unclear who is behind the wave of airline hoaxes, which come at a time of increased geopolitical tensions and warnings from authorities that Russia may be ramping up so-called hybrid threats in Europe.

Authorities have not attributed the threats to any group or state actor, and no evidence has emerged linking the hoaxes to a government. An email containing the threat sent Thursday to airport authorities in Rome and reviewed by The Associated Press purported to come from a group describing itself as anti-feminist and claiming it was targeting a “feminist regime.” Another European airport received a threat with similar wording, but it was unclear if it came from the same sender.

Bomb threats are on pilots’ minds and create unnecessary tension, but crews are prepared to respond professionally, said Paul Reuter, vice president of the European Cockpit Association. Pilots review procedures with cabin crews, identify airports where they could divert and may carry extra fuel, he said.

Reuter called the use of civil aviation for geopolitical disruption or hoaxes “totally unacceptable.”

In Ireland, the Dublin headquarters of national broadcaster RTE was evacuated Friday after a bomb threat, and live broadcasts were replaced with pre-recorded programs.

Ireland’s police force, An Garda Síochána, said it was ”aware of a threat made against media organisations here and in Europe.” It said that it has been liaising with Irish media organizations and the threat will be investigated.

Irish Prime Minister Micheál Martin said the threats to RTE and others “just illustrates how relatively simple it can be to cause disruption and to undermine the normal operation of society through unconventional activities of this kind, which are designed to cause fear and anxiety.”

He said there would be a “very significant security operation” in place next week when Dublin hosts meetings of the European Political Community and European Union leaders.

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Jill Lawless in London, Suman Naishadham in Madrid, Stephen McGrath in Leamington Spa, England, Giada Zampano in Rome, Karel Janicek in Prague, Sylvie Corbet in Paris and Mark Carlson in Brussels contributed to this report.