The Democratic National Committee offered its "deep and sincere apology" to Bernie Sanders on Monday afternoon, minutes after the party kicked off a contentious convention in Philadelphia.

Baltimore Mayor Stephanie Rawlings-Blake called the 47th Democratic convention to order just after 4 p.m., filling in for DNC Chairwoman Debbie Wasserman Schultz, who has essentially gone into exile.

The committee apologized to the senator for emails — leaked by website Wikileaks — that disparaged Sanders and suggested that top party officials favored Clinton for the party's presidential nomination.

The Wikileaks emails have roiled Sanders supporters, led to the resignation of Wasserman Schultz and deeply divided the party. Hundreds of Sanders supporters marched south of Philadelphia's City Hall, some criticizing the party.

At a pre-convention breakfast earlier Monday, attendees loudly heckled Wasserman Schultz.

Here is a partial transcript:

Wasserman Schultz: "First of all I want to ask everybody to join me in acknowledging that we had a tragic shooting in Fort Myers yesterday."

Crowd member: "How dare you?"

Wasserman Schultz: "There were children who were in harm’s way and people lost their lives."

(sound of gavel)

Wasserman Schultz: "We know something in Florida about making sure that we can have the voices across our state heard."

 

In a Pennsylvania Convention Center ballroom, Bernie Sanders addressed supporters, saying, "make no mistake about it, we have made history." He reiterated that delegates need to come together behind presumptive presidential nominee Hillary Clinton, which drew boos and angry chants from the thousand in attendance. Some yelled, "We want Bernie."

Wikileaks has not released the source of the DNC emails — which the FBI is investigating — released Friday. Some have alleged that Russian state hacked the DNC, implying that President Vladimir Putin was trying to influence the election.

"What the experts said when this breach initially happened at the DNC was that they believed it was Russian state actors who took these e-mails," Clinton campaign manager Robby Mook told CNN. "What further experts are saying is that then, because they possessed those emails, that Russian state actors were feeding the email to hackers for the purpose of helping Donald Trump."

But Donald Trump Jr., the son of the Republican nominee, rejected that allegation: "It just goes to show you their exact moral compass. They'll say anything to be able to win this. This is time and time again, lie after lie," Trump Jr. said on CNN's "State of the Union."

"It's disgusting. It's so phony," Trump Jr. said.

Later in the evening, several politicans, rights activists and celebrities took the stage, followed by first lady Michelle Obama and Massachusetts Sen. Elizabeth Warren.

Actress Sarah Silverman, who backed Sanders in the Democratic primary against Clinton, told delegates -- and a national television audience -- that she plans to vote for Clinton.

"Can I just say to the Bernie or bust people, you're being ridiculous," she said, after the crowd began to chant, "Bernie, Bernie."

As the crowd roared in applause, Minnesota Sen. Al Franken, who was standing next to Silverman, joked, "Listen to what you did."

Michelle Obama spoke of the role the president plays in the lives of children, shaping their values and aspirations, and why she believes Clinton is the leader with the ability to best fill that role.

"Because of Hillary Clinton, my daughters now take for granted that a woman can be president," she told the cheering crowd.

Sanders' speech closed out Day 1 of the Democratic National Convention.

Information from the Associated Press and CNN were used in this report.