The Associated Press is warning its reporters to stay vigilant after several received harassing messages from supporters of Democratic presidential candidate Bernie SandersBernard (Bernie) SandersSchumer: Franken should resign Franken resignation could upend Minnesota races Avalanche of Democratic senators say Franken should resign MORE.

Danny Spriggs, the AP's vice president for global security, said some reporters have received angry emails, social media messages and phone calls after the AP declared Hillary ClintonHillary Diane Rodham ClintonGrassley blasts Democrats over unwillingness to probe Clinton GOP lawmakers cite new allegations of political bias in FBI Top intel Dem: Trump Jr. refused to answer questions about Trump Tower discussions with father MORE the presumptive Democratic presidential nominee.

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"We have not received any specific security threats," Spriggs said in an email to employees, according to Poynter. "It is always good to practice situational awareness around AP bureaus and offices." 

The AP on Monday declared Clinton the Democratic nominee, saying she had enough pledged delegates and superdelegate support to reach the party's threshold for the nomination. 

Their call angered Sanders supporters, who — along with Sanders himself — argue that superdelegates shouldn't be included in the delegate count because they don't officially vote until the Democratic National Convention in July. 

The AP defended its decision to call for race for Clinton, calling the process "painstaking but very straightforward." 

"By Monday evening, 571 superdelegates had told us unequivocally that they intend to vote for Clinton at the convention. Adding that number to the delegates awarded to Clinton in primary and caucus voting to date gave her the number needed to be the presumptive nominee," Executive Editor Kathleen Carroll said in a statement.

"That is news, and reporting the news is what we do."