BEDFORD, N.Y. (AP) — A bomb was found in a mailbox at the suburban New York compound of George Soros, the liberal billionaire philanthropist who has been the target of right-wing conspiracy theorists, authorities said Tuesday.

Federal investigators were reviewing surveillance video to determine whether the package had been sent through the mail or delivered some other way, officials said, adding it was also not clear if the parcel was addressed to Soros.

A security officer at the compound about 50 miles (80 kilometers) north of Manhattan became suspicious of the package Monday afternoon and placed it in a nearby wooded area before alerting the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives, authorities said. Agents came out and safely detonated the device, which a federal law enforcement official said contained explosive powder.

"It was not a hoax device," said the official, who spoke to The Associated Press on condition of anonymity because he was not authorized to discuss the investigation.

Another federal official who also spoke on condition of anonymity said the device resembled a pipe bomb and was inside a package placed in a mailbox outside the gates of the compound. It was opened in a secure location just inside the gates, nowhere near Soros' quarters, the official said.

The Bedford Police Department said the FBI's terrorism task force was investigating.

The FBI's New York field office said on Twitter that there was "no threat to public safety" but did not respond to messages seeking comment.

A message emailed to Soros' foundation wasn't immediately returned.

Soros, who made his fortune in hedge funds, frequently donates to liberal causes. Recently, conservative critics have accused him without evidence of secretly financing the caravan of Central American migrants making their way toward the U.S.

Soros, who is Jewish, has also been the target of anti-Semitic smears. Some have falsely accused him of being a Nazi collaborator during World War II, when he was a child in Hungary.

Activists frequently post on social media the addresses of his homes, sometimes along with threats.