Threatening letter sent to Donald Trump's sister prompts investigation: Source

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Secret Service Tightens Trump's Security Amidst New Threats

Donald Trump's older sister, federal appeals court judge Maryanne Trump Barry, received a threatening letter in Philadelphia on Friday — one day after the GOP front-runner's son received a suspicious piece of mail containing white powder, sources told NBC News.

Related: N.Y. Police Investigating Suspicious Powder Sent to Donald Trump's Son Eric

There was no white powder sent to Trump Barry, although the threat included in her letter was similar to that given to Eric Trump, a source familiar with the investigation said. Eric Trump's letter, received Thursday, demanded that his real estate mogul father drop out of the Republican race for the presidential nomination.

It's unclear if both letters have the same sender. The FBI and Secret Service are investigating the incident.

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Threatening letter sent to Donald Trump's sister prompts investigation: Source
Republican presidential candidate Donald Trump responds to supporters during his rally at the University of Central Florida, in Orlando, Fla., on Saturday, March 5, 2016. (Joe Burbank/Orlando Sentinel/TNS via Getty Images)
Security removes protesters after one of many interruptions during Republican presidential candidate Donald Trump's rally at the University of Central Florida, in Orlando, Fla., on Saturday, March 5, 2016. (Joe Burbank/Orlando Sentinel/TNS via Getty Images)
Protesters interrupt Republican presidential candidate Donald Trump during his remarks at the University of Central Florida, in Orlando, Fla., on Saturday, March 5, 2016. (Joe Burbank/Orlando Sentinel/TNS via Getty Images)
ORLANDO, FL - MARCH 05: A protester yells as he is escorted out of a campaign rally for Republican presidential candidate Donald Trump at the CFE Arena during a campaign stop on the campus of the University of Central Florida on March 5, 2016 in Orlando, Florida. Primary voters head to the polls on March 15th in Florida. (Photo by Joe Raedle/Getty Images)
ORLANDO, FL - MARCH 05: People listen as Republican presidential candidate Donald Trump speaks at the CFE Arena during a campaign stop on the campus of the University of Central Florida on March 5, 2016 in Orlando, Florida. Primary voters head to the polls on March 15th in Florida. (Photo by Joe Raedle/Getty Images)
ORLANDO, FL - MARCH 05: Republican presidential candidate Donald Trump speaks at the CFE Arena during a campaign stop on the campus of the University of Central Florida on March 5, 2016 in Orlando, Florida. Primary voters head to the polls on March 15th in Florida. (Photo by Joe Raedle/Getty Images)
ORLANDO, FL - MARCH 05: Republican presidential candidate Donald Trump signs the arm of a young lady at the CFE Arena during a campaign stop on the campus of the University of Central Florida on March 5, 2016 in Orlando, Florida. Primary voters head to the polls on March 15th in Florida. (Photo by Joe Raedle/Getty Images)
A group of young Muslims stage a small protest as Republican presidential candidate Donald Trump takes the stage for a campaign rally during the Kansas GOP caucus at Century II in Wichita, Kan., on Saturday, March 5, 2016. (Bo Rader/Wichita Eagle/TNS via Getty Images)
Anti-Trump demonstrator Bill Anderson protests outside Century II, where the Republican presdential caucus took place, in Wichita, Kan., on Saturday, March 5, 2016. (Fernando Salazar/Wichita Eagle/TNS via Getty Images)
GOP presidential candidate Donald Trump addresses his supporters at rally during the Kansas GOP caucus at Century II in Wichita, Kan., on Saturday, March 5, 2016. (Bo Rader/Wichita Eagle/TNS via Getty Images)
Anti-Trump supporters demonstrate outside Century II, where the Republican presdential caucus took place, in Wichita, Kan., on Saturday, March 5, 2016. (Fernando Salazar/Wichita Eagle/TNS via Getty Images)
LOUISVILLE, KY- MARCH 5: Evelyn Stalevicz shows her support for Donald Trump as voters lined up to vote in the GOP presidential caucus at Zachary Taylor Elementary school March 5, 2016, in Louisville, Kentucky. This would be the state of Kentucky's first-ever Republican Presidential Caucus, participating in Presidential Primaries in May alongside other states. (Photo by John Sommers II/Getty Images)
Donald Trump supporters acknowledge their candidate as he takes the stage inside Century II, where the Republican presdential caucus took place, in Wichita, Kan., on Saturday, March 5, 2016. (Fernando Salazar/Wichita Eagle/TNS via Getty Images)
A Donald Trump supporter raises his sign inside Century II, where the Republican presdential caucus took place, in Wichita, Kan., on Saturday, March 5, 2016. (Fernando Salazar/Wichita Eagle/TNS via Getty Images)
Donald Trump supporters and protesters clash outside Century II, where the Republican presdential caucus took place, in Wichita, Kan., on Saturday, March 5, 2016. (Fernando Salazar/Wichita Eagle/TNS via Getty Images)
Donald Trump supporters cheer for their man inside Century II, where the Republican presdential caucus took place, in Wichita, Kan., on Saturday, March 5, 2016. (Fernando Salazar/Wichita Eagle/TNS via Getty Images)
Supporters cheer at the Trump For President rally at the University of Central Florida, in Orlando, Fla., on Saturday, March 5, 2016. (Joe Burbank/Orlando Sentinel/TNS via Getty Images)
ORLANDO, FL - MARCH 05: Republican presidential candidate Donald Trump speaks at the CFE Arena during a campaign stop on the campus of the University of Central Florida on March 5, 2016 in Orlando, Florida. Primary voters head to the polls on March 15th in Florida. (Photo by Joe Raedle/Getty Images)
WICHITA, KS - MARCH 5: A Donald Trump supporter stands in line to vote during the states Republican caucus on March 5, 2016 in Wichita, Kansas. People were standing in line for more than two hours to vote in the caucus. (Photo by J Pat Carter/Getty Images)
WICHITA, KS - MARCH 5: A man shows his support as Republican presidential candidate Donald Trump made a speech at a campaign rally on March 5, 2016 in Wichita, Kansas where the Republican party was staging one of its statewide caucus. Trump spoke of making America great again. (Photo by J Pat Carter/Getty Images)
WICHITA, KS - MARCH 5: Republican presidential candidate Donald Trump makes a speech at a campaign rally on March 5, 2016 in Wichita, Kansas. The Republican party was holding its state wide caucus in several locations. (Photo by J Pat Carter/Getty Images)
WICHITA, KS - MARCH 5: An anti-Trump protester stands outside the convention center where Republican presidential candidate Donald Trump made a speech at a campaign rally on March 5, 2016 in Wichita, Kansas. About 100 protesters voiced their opposition to Trump. (Photo by J Pat Carter/Getty Images)
WICHITA, KS - MARCH 5: A veteran showed his support as Republican presidential candidate Donald Trump made a speech at a campaign rally on March 5, 2016 in Wichita, Kansas where the Republican party was staging one of its statewide caucus. Trump said he would help veterans. (Photo by J Pat Carter/Getty Images)
A protester chanting "Black Lives Matter" is escorted away as Republican presidential candidate Donald Trump, background, speaks at a campaign rally in New Orleans, Friday, March 4, 2016. (AP Photo/Gerald Herbert)
WICHITA, KS - MARCH 5: Supporters displays their signs as Republican presidential candidate Donald Trump makes a speech at a campaign rally on March 5, 2016 in Wichita, Kansas. The Republican party was holding its state wide caucus in several locations. (Photo by J Pat Carter/Getty Images)
Republican presidential candidate Donald Trump holds up a child he pulled from the crowd as he arrives to speak at a campaign rally in New Orleans, Friday, March 4, 2016. (AP Photo/Gerald Herbert)
Republican presidential candidate Donald Trump speaks at a campaign rally in New Orleans, Friday, March 4, 2016. (AP Photo/Gerald Herbert)
Republican presidential candidate Donald Trump speaks at a campaign rally in New Orleans, Friday, March 4, 2016. (AP Photo/Gerald Herbert)
Republican presidential candidate Donald Trump speaks at a campaign rally in New Orleans, Friday, March 4, 2016. (AP Photo/Gerald Herbert)
A protester and activist holds a sign for the "Islam Against Terrorism" before a campaign rally, Saturday, March 5, 2016, in Orlando, Fla. (AP Photo/Brynn Anderson)
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Trump Barry, a 78-year-old judge with the U.S. Circuit Court of Appeals for the 3rd Circuit, was the subject of some scrutiny earlier this year when Trump mentioned her in jest when asked about whom he would appoint to the Supreme Court.

Rival Ted Cruz, meanwhile, called Trump Barry a "radical pro-abortion extremist" for her ruling against banning abortions in New Jersey.

The mail sent to Eric Trump was postmarked in Massachusetts, police sources said, but preliminary tests deemed the substance non-hazardous.

Calls for suspicious and threatening packages are common for high profile personalities.

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