By Inti Landauro 

PARIS--French authorities Tuesday were trying to hunt down the pilots of drones that were spotted flying over Paris landmarks and high-security buildings including the U.S. embassy.

The small, remotely-controlled flying objects were seen overnight Monday to Tuesday over the U.S. embassy and nearby Interior Ministry, as well as over the Eiffel tower nearly 2 miles to the west and Place de la Bastille over 2.5 miles to the east.

The Paris prosecutor has asked French police to open an investigation as flying drones over urban areas is banned in France, a spokeswoman for the prosecutor said.

It isn't the first time France has been rattled by suspicious drone flights. In October last year, highly-secured nuclear power stations operated by power utility Electricité de France SA were also buzzed by mysterious drones. Last month, a drone was spotted flying briefly over the Élysée Palace, President François Hollande's official residence.

While the investigation in Paris isn't related to antiterrorism, the flights come as the capital remains on high alert after terror attacks in January. Soldiers and armed police have maintained a heavy presence in front of state buildings and embassies around the capital.

Remote-controlled drones--small, unmanned aerial vehicles--are available commercially and are popular in France. The array of drone flights spotted in the country in recent months has raised concerns that they are being used for surveillance purposes.

An official at the U.S. embassy declined to comment on the drone flights.

Police have no evidence to explain the purpose of the flights over Paris, a police officer said. The authorities don't know how many drones were involved or whether there was any coordination between the flights, he said.

William Horobin contributed to this article.

Write to Inti Landauro at inti.landauro@wsj.com

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