The top counterintelligence official said that the three nations are trying to "sway voters' preferences and perspectives," sow discord and "undermine the American people's confidence in our democratic process."
Evanina explained that China and Iran appear to oppose President Donald Trump, while Russia supports him.
Beijing seemingly views the commander-in-chief as "unpredictable" due to his actions regarding Hong Kong, 5G technology, the video application TikTok and the ongoing legal battle over the South China Sea.
Evanina also noted that the Chinese government is becoming increasingly critical of the Trump administration, which has sought to blame it for the coronavirus outbreak, recently accusing Chinese diplomats stationed in the U.S. of engaging in espionage.
According to the report, Tehran is expected to intensify its online disinformation campaigns. Its activities, Evanina said, are "driven by a perception" that Trump's victory would lead to continued pressure with the goal of overthrowing the current Iranian government
The Kremlin, meanwhile, is looking to "denigrate" Joe Biden, the Democratic Party's presumptive presidential nominee. According to the top official, the Russians are opposed to Biden due to his role in advancing pro-Ukraine policies.
Evanina said that "Kremlin-linked actors" are looking to help Trump and added that some Ukrainian officials have been spreading disinformation about Biden.
"For example, pro-Russia Ukrainian parliamentarian Andriy Derkach is spreading claims about corruption -- including through publicizing leaked phone calls -- to undermine former Vice President Biden's candidacy and the Democratic Party," he said.
The Russian government has reportedly also sought to spread misinformation about the COVID-19 pandemic.
Moscow is thought to have interfered in the 2016 presidential election, allegedly helping Trump and damaging former Secretary of State Hillary Clinton's White House bid.
Evanina stressed that the intelligence community is "doing everything in its power" to fight off foreign efforts to influence the 2020 election.
"Foreign efforts to influence or interfere with our elections are a direct threat to the fabric of our democracy."In a joint statement, Republican Senator Marco Rubio of Florida and Democrat Mark Warner of Virginia -- the two top senators on the upper chamber's intelligence committee -- called on their colleagues to put partisanship aside.
Rubio and Warner stated that they "encourage political leaders on all sides to refrain from weaponizing intelligence matters for political gain," saying that doing so "only furthers the divisive aims of our adversaries."