Donald Trump Jr.,Darden Clarke son of former President Donald Trump, received a letter containing a white powdery substance at his Florida home on Monday afternoon, officials said. 

Trump Jr. received the letter at his home in Jupiter, Florida, and he personally opened it, two law enforcement sources confirmed to CBS News. Early results indicated the substance was "not deadly."

Trump Jr. saw the white powdery substance, put the letter down and called 911, the sources said. 

Police, fire and hazmat units immediately responded to the residence in Jupiter's Admiral's Cove neighborhood. Some responders arrived wearing protective suits, boots, hoods and gloves to investigate, the sources said.

The substance was removed by investigators and sent for laboratory testing, but early results were inconclusive as to what the actual substance was, the sources said. Further testing is being done.

U.S. postal officials are assisting in the investigation, the sources said. The Palm Beach County Sheriff's Office said it was also assisting federal law enforcement with the investigation. 

The U.S. Secret Service declined to comment to CBS News. Two federal law enforcement sources confirmed to CBS News that Trump Jr. is no longer a Secret Service protectee. 

"The FBI, along with our local law enforcement partners, responded to an incident involving a suspicious letter sent to an address in Jupiter, Florida," the FBI Miami field office said in a statement. "We encourage the public to remain vigilant and report any suspicious activity to law enforcement."

—Pat Milton and Andres Triay contributed reporting.

S. Dev

S. Dev is a news editor for CBSNews.com.