The U.S. Postal Service intercepted a suspicious envelope containing a foreign substance before it reached Rep. Donald Norcross's Cherry Hill district office on Monday, Oct. 19.

The envelope was addressed to Norcross's office at 10 Melrose Ave., according to Cherry Hill Patch.

Norcross, a Democrat representing New Jersey's 1st Congressional District, said he was grateful to the Postal Service and law enforcement for identifying the threat.

"A single threat against one elected official is chilling enough," Norcross said. "But it's more common than ever that elected officials and their staff - no matter their title nor party - are being targeted for no other reason than choosing public service."

The Cherry Hill incident is part of a broader wave. Four other New Jersey lawmakers confirmed their offices received suspicious mail in recent days, Patch reported. U.S. Reps. Bonnie Watson Coleman, Rob Menendez, Frank Pallone and Analilia Mejia all reported suspicious packages at their district offices.

Nationwide, the scope is wider still. Law enforcement sources told ABC News that over 100 letters containing white powder may be circulating in the U.S. mail system, 6ABC reported. None of the envelopes received by congressional offices have tested positive for hazardous substances, according to 6ABC.

The FBI confirmed it is working with the U.S. Postal Inspection Service to investigate what it called "a series of suspicious mailings sent to various addresses nationwide," according to CQ Roll Call. The targets include Secretary of State offices and election offices.

House Sergeant at Arms William McFarland warned in a memo to members and staff that more offices may receive similar letters "in the coming days," Roll Call reported. The memo instructed staff to use safe mail-handling procedures, including mail hoods provided by the Sergeant at Arms.

Lawmakers on both sides of the aisle have been targeted. Republican Sen. Ted Cruz of Texas and Democratic Sen. Chuck Schumer of New York are among those who received threatening packages, NBC News reported.

Photos shared by some lawmakers showed "DSA" in the upper left corner alongside a return address once tied to the Democratic Socialists of America. The group denied involvement, with a spokesperson telling The New York Times that "D.S.A. did not send these letters," Roll Call reported.

Investigators have not publicly identified a suspect or motive. The interception at Norcross's office came two weeks before the Nov. 3 general election.

Residents who receive suspicious mail should avoid handling it and call 911 or the U.S. Postal Inspection Service at 877-876-2455.