White supremacists will remain the most "persistent and lethal threat"  to the US through 2021, a draft document from the Department of Homeland Security (DHS) has revealed.

The document is the first of the three draft versions released by Brookings senior fellow Benjamin Wittes of the same State of the Homeland Threat Assessment 2020, reports Xinhua news agency.

The later two versions describe the threat from white supremacists with slightly different wording, but all the three drafts state that white supremacist extremists are the deadliest threat and list it above the immediate danger from foreign terrorist groups.

Although foreign terrorist groups will continue to call for attacks on the US, they "probably will remain constrained in their ability to direct such plots over the next year", all three documents said.

Russia "probably will be the primary covert foreign influence actor and purveyor of disinformation and misinformation in the Homeland", they added.

Wittes posted all the three versions on Twitter earlier this month, saying: "I made this material public because I wanted there to be a benchmark about what the career folks at DHS actually assessed the threats to be against which we can measure whatever the administration actually chooses to release."

The annual threat assessment has not yet been published by the DHS.