DNC: Bernie Sanders campaign improperly accessed confidential Hillary Clinton voter information

US Senator Bernie Sanders' presidential campaign improperly accessed confidential voter information from Democratic rival Hillary Clinton's campaign, according to Democratic National Committee officials.

The Washington Post first reported the DNC charges Thursday evening.

Sanders campaign manager Jeff Weaver told WaPo that a low-level staffer did view Clinton voter information and that one staffer had been fired over the incident. It was unclear if the fired staffer was the same person who viewed the information.

Weaver blamed the illicit viewing on a glitch from software supplied by a DNC-hired vendor.

The incident has "sparked alarm at the DNC," according to WaPo, and the organization has cut off the Sanders campaign from its list of likely Democratic voters.

"The decision by the party committee is a major blow to Mr. Sanders's campaign," The New York Times reports. "The database includes information from voters across the nation and is used by campaigns to set strategy, especially in the early voting states."

Hillary Clinton's campaign declined to comment, according to WaPo.

The Democratic candidates are set to debate Saturday night, their third meeting this election.