Security Concerns Raised for Democratic National Convention After Nevada

— -- Security preparations for the Democratic National Convention have been underway for months, but there's a new level of concern in light of violence that broke out at last Saturday’s state convention in Nevada.

Sen. Dianne Feinstein said today that the violence "worries me a great deal" and referred to the 1968 Democratic Convention in Chicago. Riots broke out during that convention, and police confrontations with protesters were widely reported.

"I don't want to go back to the '68 convention, because I worry about what it does to the electorate as a whole, and he should too," Feinstein said of Sen. Bernie Sanders.

The Democratic National Committee (DNC) issued a statement Tuesday saying it is "deeply concerned" about what happened at the Nevada convention, and it called on the Sanders' and Hillary Clinton's campaigns to "ask them to stand with the Democratic Party in denouncing and taking steps to prevent the type of behavior on display over the weekend in Las Vegas."

Sanders said Tuesday that party leaders in Nevada had been saying that his campaign "has a 'penchant for violence.' That is nonsense."

"Our campaign has held giant rallies all across this country, including in high-crime areas, and there have been zero reports of violence. Our campaign of course believes in nonviolent change, and it goes without saying that I condemn any and all forms of violence, including the personal harassment of individuals," Sanders said.

One individual who was harassed was Roberta Lange, the Nevada Democratic Party chairwoman, who received threatening voice mails and text messages from Sanders supporters.

"I hope you are taken out on a stretcher when Philly riots," read one such text message, obtained by ABC News.

Earlier in the presidential campaign, there was concern that violence would break out at the Republican National Convention, which will be held in Cleveland a week before the Democrats' event in Philadelphia.

In March, Donald Trump warned that there may be riots in Cleveland if the Republican Party tried to stop him from becoming the nominee at a contested convention. Now it's Sanders' supporters threatening violence, with chairs being thrown and threats being issued.

Steve Gomez, a former special agent in charge of counterterrorism for the FBI in Los Angeles who now works as a consultant for ABC News, said that it would be fair to expect that more than 1,000 law enforcement officers and agents will be involved with security for the convention in Philadelphia, which takes place from July 25 to 28.

"It's really important that they [law enforcement] start to evaluate the past instances where there's been protests, riots and violence because they need to see who were the people who were involved in that. Were they a certain segment of Sanders supporters or Clinton supporters?" Gomez told ABC News.

The Philadelphia Police Department has not released any information about its security plans and did not immediately respond to ABC News' requests for comment.

Five groups supporting Bernie Sanders' presidential campaign have recently filed permit applications with the city of Philadelphia to protest near the site of the convention. Only nine applications have been filed so far with the city.

According to the Philadelphia Office of the Mayor, the protests will take place near the Wells Fargo Arena in a designated protest zone.

Gomez said security preparations for the convention were likely underway ever since arena, home to the Philadelphia Flyers hockey team and the 76ers basketball team, was announced as the site in February 2015.

"Once the campaign started to kick off, there were probably multiagency working groups, including law enforcement, the fire department, emergency management and probably some state agencies," he said.

ABC News' Seniboye Tienabeso contributed to this report.