China would prefer that President Donald Trump not win a second term in the November election, while Russia is seeking to "denigrate" Trump's opponent and former Vice President Joe Biden, a top U.S. counterintelligence official said Friday.

The intelligence assessment was announced as part of efforts to alert the U.S. public about how foreign states may seek to sway voters' preferences and increase discord in the country, with particular concern expressed over potential activities by China, Russia and Iran.

Combined file photo shows U.S. President Donald Trump (L) and Chinese President Xi Jinping. (Kyodo)

China sees Trump as "unpredictable" and would prefer his defeat in the election, William Evanina, director of the National Counterintelligence and Security Center, said in a statement.

"China has been expanding its influence efforts ahead of November 2020 to shape the policy environment in the United States, pressure political figures it views as opposed to China's interests, and deflect and counter criticism of China," he said.

The official also suggested an increasing frustration on Beijing's side over a series of actions the Trump administration has taken to oppose them on issues involving Hong Kong, the disputed South China Sea and next-generation 5G technology, which China leads.

On Russia, which allegedly interfered in the 2016 U.S. election to boost Trump's prospects, Evanina said Moscow is using "a range of measures to primarily denigrate former Vice President Biden and what it sees as an anti-Russia 'establishment.'"

"Some Kremlin-linked actors are also seeking to boost President Trump's candidacy on social media and Russian television," he said.

Undated combined photo shows Russian President Vladimir Putin (R) and U.S. President Donald Trump. Putin will meet Trump in July 2017 on the fringes of a Group of 20 summit to be held in Germany, Russian Foreign Minister Sergey Lavrov said on May 10. (Getty/Kyodo)

Iran is also seeking to undermine Trump's re-election bid, believing that his second term would mean a continuation of U.S. pressure on Iran in an effort to foment regime change.

Iran's efforts will likely focus on online influence, such as spreading disinformation on social media and recirculating anti-U.S. content, the official warned.