Iran is denying reports it was involved in attempts to hack the presidential campaigns of former President Donald Trump and President Joe Biden, the latter of which while he was still in the race.

In a statement, the Permanent Mission of the Islamic Republic of Iran to the United Nations, said that reports of attempted hacking, which came from Google and Microsoft, are "unsubstantiated."

"Such allegations are unsubstantiated and devoid of any standing. As we have previously announced, the Islamic Republic of Iran harbors neither the intention nor the motive to interfere with the U.S. presidential election," the statement read. "Should the U.S. government genuinely believe in the validity of its claims, it should furnish us with the pertinent evidence—if any—to which we will respond accordingly."

-ABC News' Pierre Thomas

Lowering health care costs will be a central theme at the Democratic National Convention this week, campaign and convention officials said on Monday, with Sen. Bernie Sanders (I-Vt.), confirmed as one notable program speaker set to focus upon the issue -- specifically on "lowering Rx drug prices" and "taking on Big Pharma."

Speakers throughout the week like Sanders, California Rep. Robert Garcia, Illinois Rep. Lauren Underwood and New Mexico Gov. Michelle Lujan Grisham will highlight the support of Vice President Kamala Harris and Minnesota Gov. Tim Walz for strengthening the Affordable Care Act, convention officials shared first with ABC News.

In a Friday speech setting out a string of economic proposals, Harris pledged to "lower the cost of insulin and prescription drugs for everyone." She also said she'd "demand transparency from the middlemen who operate between Big Pharma and the insurance companies, who use opaque practices to raise your drug prices and profit off your need for medicine."

-ABC News’ Isabella Murray

Actors Kerry Washington, Tony Goldwyn, Mindy Kaling and commentator Ana Navarro will serve as hosts at the Democratic National Convention this week, convention officials confirmed to ABC News.

Each will host one night of the four-day convention, starting the programming with opening remarks and reappearing onstage throughout the night.

Goldwyn will host Monday night, Navarro on Tuesday and Kaling on Wednesday. Washington will host on Thursday, the night Vice President Kamala Harris formally accepts her nomination.

CNN first reported this news.

Vice President Kamala Harris and Gov. Tim Walz debuted their new campaign buses Sunday and kicked off a bus tour of southwestern Pennsylvania ahead of this week's Democratic National Convention.

Upon their arrival on Air Force Two, a few hundred supporters greeted Harris, Walz and their spouses at a hangar where the new were buses parked.

Supporters told ABC News they were thrilled by Harris' candidacy, with one saying she had not felt this excited about politics in years. Some said they had never volunteered for a campaign before signing up to work on Harris'.

"I was excited about Biden, but I am a million times more excited about Kamala," Nicole Molinaro, a Pittsburgh-area mom, said. "I think that we need her leadership. We need her intelligence. We need her progressive, you know, stance. I think we need her experience. We need everything about Kamala."

Another supporter, Edward Freel, said he was unsure about Harris at first, "but then, as I started listening better and following her, [I thought] this woman is going to be good for this country."