An explosive device was discovered in the mailbox outside the home of billionaire financier and philanthropist George Soros, authorities confirmed on Tuesday.

Soros, a political activist and major donor to liberal causes, has been a favorite target for rightwing groups and conspiracy theories, and a magnet for criticism from Donald Trump.

An employee at the home in Katonah, an affluent suburb in wealthy Westchester county, just north of New York City, opened a package that had been left in the mailbox, and found the device. The staff member took the parcel away from the home into a nearby area with trees and undergrowth, then alerted law enforcement.

Bomb squad technicians detonated the package in the wooded area, police told the New York Times. Soros was not home at the time.

On Tuesday afternoon, a spokeswoman for George Soros’s charitable network, Open Society Foundations, issued a statement from the financier urging politicians to “tone down their rhetoric”. Spokeswoman Laura Silber said Soros is calling for a “more civil way’” to discuss political differences.

Earlier, a law enforcement official said that the device “had the components” of an actual bomb, including explosive powder. “The components were there for an explosive device,” the official told the Associated Press, adding it was “not a hoax device”.

The Bedford police department received a call at about 3.45pm on Monday about the suspicious package in the mailbox, police said in a statement. Katonah is a hamlet within the town of Bedford.

“An employee of the residence opened the package, revealing what appeared to be an explosive device,” the department said. “The employee placed the package in a wooded area and called the Bedford police.”

The case has been turned over to the FBI, which is investigating through its joint terrorism taskforce. “We are conducting an investigation at and around a residence in Bedford, NY. There is no threat to public safety, and we have no further comment at this time,” the FBI’s New York field office said on Twitter.

Investigators are reviewing surveillance video to determine whether the package had been sent through the mail or otherwise delivered, the law enforcement official said. There were no immediate arrests.

Soros, who was born in Hungary, has given money to Democratic candidates and progressive causes after making his billions running a hedge fund.

He has become an arch-enemy of the right, and the address of his home has often been posted on social media along with derogatory comments.

Soros, who is Jewish, has also been the target of antisemitic comments and conspiracy theories.

Trump has targeted him as well, claiming without evidence that protesters opposing the supreme court nomination of Brett Kavanaugh were “paid by Soros and others”.

Most recently, Soros has been falsely blamed for paying Central American migrants to join a caravan of people attempting to travel to the United States. The Florida congressman Matt Gaetz posted a video that claimed women and children being given cash to “storm the US border at election time” and suggested without evidence that the source could be “Soros? US-backed NGOs?”

Soros has also been the target of a hostile media campaign by the nationalist government in his native Hungary.