Prosecutors boosted charges Tuesday against four men accused after an elaborate FBI sting operation of plotting to bomb New York City synagogues and shoot down military airplanes.

The charges were described in an eight-count indictment returned in U.S. District Court.

The men originally were charged with conspiracy to use weapons of mass destruction and conspiracy to acquire and use anti-aircraft missiles. Tuesday's indictment added three counts of attempting to use weapons of mass destruction, a charge alleging an attempt to acquire and use anti-aircraft missiles and two charges alleging a conspiracy to kill U.S. officers and employees and attempting to kill officers and employees.

An arraignment was scheduled for Wednesday on the charges, most of which carry a potential penalty of life in prison.

The men, arrested May 20, were accused by prosecutors of plotting for the last year to carry out acts of terrorism out of hatred for Jews and America.

Authorities said the lethal explosives and a surface-to-air missile system that the men thought they had obtained actually were inert devices supplied by the FBI in a sting operation.

Prosecutors say the men plotted to destroy two synagogues in the heavily Jewish Riverdale section of the Bronx and to shoot down planes at the Air National Guard base in Newburgh, about 50 miles north of New York City.

The four men, James Cromitie, David Williams, Onta Williams and Laguerre Payen, are held without bail in Westchester County, just north of the city. They haven't entered pleas yet.

Relatives have said the defendants were struggling men who had worked at places such as Wal-Mart, a landscaping company and a warehouse.