US Democratic presidential candidate Bernie Sanders has apologised to frontrunner Hillary Clinton during a debate for a breach of her campaign's voter files by one of his staffers.
Mrs Clinton, whose campaign had said Mr Sanders made a number of breaches into its computer files, accepted the apology and said it was time to move on.
The two candidates, and a third, former Maryland governor Martin O'Malley, also debated how to take on Islamic State militants and protect Americans from attacks like this month's killings of 14 people in a shooting spree in San Bernardino, California.
Mr Sanders is trying to erase Mrs Clinton's lead just six weeks before the Democrats' first nominating contest in Iowa, ahead of the country's presidential election in November 2016.
Strategically crucial database
Bernie Sanders said there were computer breaches - which he said were the fault of the software vendor - on two occasions, in which his campaign could see proprietary data from Mrs Clinton's campaign, and that they alerted party officials "quietly".
The candidate said his campaign "didn't run to the media and make a big deal about it".
He said the most recent breach involved inappropriate behaviour by one of his staff members, adding that person had now been dismissed.
Mr Sanders said the Democratic Party's decision to temporarily suspend his campaign's access to the strategically crucial database at the centre of the incident was "an egregious act".
On Friday, his campaign filed a lawsuit against the Democratic National Committee (DNC) in a federal court to restore its access to it.
The database contains strategically important information on voters, which campaigns use to decide strategy. It takes on a crucial role as campaigns prepare for early primary voting.
The DNC maintains the database and charges campaigns for access.
Guns 'will not make America safer'
Gun control and the fear of terror attacks in the US were also tackled in today's debate.
"Guns in and of themselves will not make America safer," Mrs Clinton said. "Arming more people… is not the appropriate response to terrorism."
Mrs Clinton said Republican rhetoric - especially from Donald Trump - was "fanning the flames of radicalisation".
She said Islamic State militants were showing videos of the billionaire tycoon talking about his proposed ban on Muslims entering the US as a recruitment tool.
But Mr O'Malley accused his two rivals of "flip-flopping" in Washington over gun ownership restrictions.
For his part, Mr Sanders said US foreign policy needed to focus on destroying Islamic State, not removing Bashar al-Assad from power in Syria.
"It is not Assad that is attacking the United States," he said. "First priority: destroy ISIS [Islamic State]."
Mr Sanders also criticised Qatar, saying that "instead of spending $200bn ($NZ297bn) on the World Cup, maybe they should pay attention to ISIS on their doorstep".
- BBC / Reuters