An explosive device was found Monday in a mailbox at the New York residence of George Soros, a liberal philanthropist and target of far-right nationalist groups, authorities said.

The Bedford Police Department said a suspicious package was discovered Monday afternoon by an “employee of the residence.” Police didn’t specify who owned the home, but town records show that it is co-owned by Soros Fund Management, a family office operated by Soros. Inside the package was what appeared to be an explosive device, police said. The employee placed the material in a wooded area and notified authorities at 3:45 p.m. Monday.

Authorities in Bedford — which includes the hamlet of Katonah, where the residence is located — said an “extensive investigation commenced,” also involving the Westchester County Police Department, the federal Bureau of Alcohol, Tobacco, Firearms and Explosives, and the FBI. The case has since been turned over to the FBI’s Joint Terrorism Task Force. The FBI’s New York office said in a tweet late Monday that it was investigating and that there was no threat to the public.

The Open Society Foundations, a philanthropic organization run by Soros, didn’t immediately return a request for comment. The Times of Israel reported that Soros, a billionaire hedge fund manager and prominent donor to Democratic and other causes, was not home at the time.

The 88-year-old Holocaust survivor has funneled much of his fortune into liberal projects worldwide, including in his native Hungary, which has taken an illiberal, nationalist turn under Prime Minister Viktor Orban. After he won reelection in April, Orban wasted no time in pushing a “Stop Soros” bill designed to crack down on nongovernmental organizations, think tanks and other liberal institutions. Justified in the name of deterring illegal immigration, the measure was passed in June.

The Hungarian government’s attack on Soros, which relies on anti-Semitic tropes, has fed into a conspiracy theory that casts the Jewish philanthropist as the director of a global cabal intent on flooding the West with migrants and undermining national sovereignty. Soros has become an archrival invoked by autocrats and far-right activists worldwide.

President Trump bought into the conspiracy theory this month when he tweeted that protesters opposing the nomination of Brett M. Kavanaugh to the Supreme Court were “paid for by Soros and others.”

It was a claim also made by Sen. Charles E. Grassley (R-Iowa), the chairman of the Senate Judiciary Committee, and by Rudolph W. Giuliani, a lawyer for Trump. Giuliani, a former mayor of New York, retweeted a message calling Soros the “anti-Christ.”