The Democratic National Committee offered its “deep and sincere apology” to Bernie Sanders, his supporters and the entire party for what it calls “the inexcusable remarks made over email”.
The statement from incoming interim party leader, Donna Brazile, and six other officials said the comments in the emails “do not reflect the values of the DNC or our steadfast commitment to neutrality during the nominating process”.
The statement said the party will not tolerate disrespectful language.
The statement was not signed by the ousted DNC head, Debbie Wasserman Schultz.
The Florida congresswoman announced on Sunday that she would step down from that job at the end of this week’s Democratic National Convention in Philadelphia.
The emails suggested party officials favoured Hillary Clinton over rival Mr Sanders during the primaries.
The apology came as the Democrats got their convention under way in Philadelphia.
It was Baltimore’s mayor, Stephanie Rawlings-Blake, who called the 47th Democratic convention to order. Her formal welcome was briefly held up a slight oversight – she forgot the gavel and had to retrieve it off stage.
Ms Rawlings-Blake is a last-minute replacement for Ms Wasserman Schultz.
Ms Rawlings-Blake serves as secretary of the DNC.