BEIJING - China and Russia pose the biggest risks to the United States, and are more aligned than they have been in decades as they target the 2020 presidential election and American institutions to expand their global reach, US intelligence officials told senators on Tuesday.

The spy chiefs broke with President Donald Trump in their assessments of the threats posed by North Korea, Iran and Syria. But they outlined a clear and imminent danger from China, whose practices in trade and technology anger the US president.

While China and Russia strengthen their alliance, Director of National Intelligence Dan Coats said some American allies were pulling away from Washington in reaction to changing US policies on security and trade.

The directors of the CIA, FBI, National Security Agency and other intelligence agencies flanked Coats at the Senate Intelligence Committee hearing. They described an array of economic, military and intelligence threats, from highly organised efforts by China to scattered disruptions by terrorists, hacktivists and transnational criminals.

"China, Russia, Iran, and North Korea increasingly use cyber operations to threaten both minds and machines in an expanding number of ways - to steal information, to influence our citizens, or to disrupt critical infrastructure," Coats said.

"Moscow's relationship with Beijing is closer than it's been in many decades," he told the panel.

The intelligence officials said they had protected the 2018 US congressional elections from outside interference, but expected renewed and likely more sophisticated attacks on the 2020 presidential contest.

US adversaries will "use online influence operations to try to weaken democratic institutions, undermine alliances and partnerships, and shape policy outcomes," Coats said.(FA)