Paris (AFP) - Investigators in Paris have been left puzzled by a string of drone sightings over Paris, even as three journalists for TV station Al-Jazeera were arrested Wednesday for flying one from a park on the edge of the city.

Witnesses and security forces reported at least five sightings overnight Tuesday to Wednesday and a similar number the night before.

Then, on Wednesday, police arrested the Al-Jazeera trio in the Bois de Boulogne.

"The first was piloting the drone, the second was filming and the third was watching," a judicial source told AFP.

Although there was no suggestion they were linked to the series of earlier drone sightings, they come at a time when the city is still on high alert following last month's jihadist attacks.

Those unexplained sightings were made near the US embassy, not far from the Invalides military museum, the Eiffel Tower and several major thoroughfares leading in and out of the French capital, a police source said.

The names and nationalities of the three journalists from Al-Jazeera's international service were not given. They are aged 34, 52 and 68.





- Multiple drone sightings -





Police had been unable to catch any of the operators of the night-time flights and it was unclear whether they were the work of pranksters, tourists or something more malicious.

"People should not be worried but vigilant, it's an issue which is taken very seriously," government spokesman Stephane Le Foll told reporters.

He said drone flyovers had taken place in other countries such as Germany, where a small unmanned aircraft operated by activists denouncing police surveillance landed just metres away from Chancellor Angela Merkel during a 2013 campaign event.

And last month in Washington, a small drone crash-landed on the grounds of the White House, prompting a security lockdown.

French authorities were first alerted to mystery drone flyovers in October, when state-run power company EDF filed a complaint with police after detecting the small aerial vehicles zipping over seven atomic plants.

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The sightings continued into November, and altogether some 20 flyovers took place over nuclear plants. Their operators were never found.

In October, a 24-year-old Israeli tourist spent a night in jail and was slapped with a 400-euro ($450) fine for flying a drone above the Notre Dame cathedral.

Then on January 20, a pilotless aircraft briefly went over the presidential palace in Paris, not long after jihadist attacks in and around the French capital that left 17 people dead and put the country on high alert.

In late January, small drones were also spotted near a bay in Brittany that houses four nuclear submarines -- one of the most protected sites in the country.





- 'Eye on the sky' -





With many more police and troops out on the streets of Paris following the January shootings, drone sightings may be more likely.

"Many sensitive sites are protected and from now on we are asking law enforcement to have an eye on the sky as well," said a police source.

French law prohibits small civilian drones from sensitive areas such as nuclear facilities, which are protected by a no-fly zone that spans a 2.5-kilometre (1.6-mile) radius and a height of 1,000 metres.

Faced with the difficulty of intercepting drones and their operators, France has launched a one-million-euro programme aimed at developing ways of dealing with them.