Donald Trump has relied upon a dubious statistic to support his ban on travel to the US from seven majority-Muslim countries, terrorism researchers and databases indicate.

Trump, in his Tuesday night address to Congress, cited unspecified data from the Department of Justice to claim that the “vast majority” of people convicted of terrorism-related offenses in the US since 9/11 “came here from outside of our country”.

Ahead of unveiling a new version of the ban in the coming days, Trump marshalled the statistic to contend that his draconian approach was necessary to prevent a “beachhead of terrorism” inside the US.

Though Trump did not specify the source for his data, several terrorism scholars have identified it as a justice department compilation released last year by Jeff Sessions, now Trump’s attorney general. Neither the justice department nor the White House responded to requests from the Guardian about the statistics.

However, several leading terrorism scholars cautioned that the convictions data in the Sessions document painted an inaccurate picture of terrorism in the United States.

“Those figures are technically correct if you count only international terrorism-related cases as calculated by the Department of Justice, but it is substantively misleading because it doesn’t include domestic terrorism and it does include a large number of cases that pose no threat to the United States,” said Charles Kurzman, a University of North Carolina professor who tallies data on American Muslim extremists.

“That would include people attempting to travel abroad, financing of movements abroad, sometimes in very small amounts, and a couple hundred cases from the years right after 9/11, with no known link to terrorism, that are nonetheless included on that list.”

The thinktank New America Foundation also keeps a database of those charged with terrorism – not only those convicted of it – in federal courts since 9/11. It focuses on Sunni jihadist terrorism such as efforts by al-Qaida and Isis, excluding terror organizations such as Colombia’s Farc or Lebanon’s Hezbollah, as well as white-supremacist terrorism in the US.

According to New America’s database, 84% of jihadist terrorism-related offenses in the US since 9/11 are attributable to US citizens or permanent residents. A quarter of such offenders, New America’s researchers found, are converts, “further confirming the challenge cannot be reduced to one of immigration”.

Data kept by the University of Maryland’s National Consortium for the Study of Terrorism and Responses to Terrorism (Start) backs up the New America finding.

One of its datasets, Profiles of Individual Radicalization in the United States (Pirus) goes far beyond jihadist terrorism, to study 1,500 individuals radicalized in the US from 1948 to 2013. Its definition of radical extremism is far broader than the “radical Islamic terrorism” formulation Trump embraces, including far-right and far-left terrorism. Approximately 90% of its cases are US citizens, and the vast majority natural-born, according to the Pirus researcher Patrick James.

Restricting the data to post-9/11 instances of domestic radicalization to Sunni jihadist terrorism – also a category broader than terrorism convictions – James found that of 207 cases, 109 were natural-born American citizens. The remaining 98 cases were first-generation immigrants radicalized inside the US. Since the breakdown is in roughly the same proportion to the broader US Muslim community, James said, “you can’t say the first generation is more of an at-risk community”.

A protest march in New York against the travel ban, which was halted by a US court . A new version of the ban is set to be unveiled soon.

Similarly, an intelligence report from the Department of Homeland Security (DHS) undercuts the premise of Trump’s ban on immigration from seven majority-Muslim countries. DHS’s bureau of intelligence and analysis (I&A) concluded that “country of citizenship is unlikely to be a reliable indicator of potential terrorist activity”.

Citing US justice department press releases on convictions since the Syrian civil war began in 2011, DHS intelligence analysts found that “slightly more than half” of 82 people identified as convicted of terrorism offenses in the US or killed in the pursuit of them were “native-born United States citizens”.

Citizens of the seven banned countries were “rarely implicated in US-based terrorism”. Iran, Sudan and Yemen each had one. Syria had none. Somalia had three such citizens; Iraq, which Trump is considering exempting from the revised ban, had two.

Gillian Christensen, a DHS spokesperson, dismissed the analysis as “commentary from open source reporting versus an official, robust document with thorough interagency sourcing. The I&A report does not include data from other intelligence community sources. It is clear on its face that is an incomplete product that fails to find evidence of terrorism by simply refusing to look at all the available evidence.”

Several researchers believe Trump’s citation derived from a June 2016 Senate subcommittee tally tallying 580 people convicted of terrorism-related charges from 9/11 to 2014. That tally, led by then-senator Sessions, found 73% of convicts were foreign born.

The University of Maryland’s James called the tally a “dubious” overcount.

“Just looking at some of the cases, a lot of them weren’t charged with anything related to terrorism. Sometimes bringing a case to court, they’ll just be charged with something like illegal weapons possession or fraud or embezzlement that they may think had something to do with terrorism, but it’s not actually brought to court, so it becomes hard to count. It becomes kind of a moving target,” James said.

The New America Foundation’s David Sterman said Trump was applying “a kitchen-sink approach to cases that are often neither actually terrorism cases nor cases that demonstrate a need for the travel ban” but instead “justify his preferred policy position, when more detailed examination of the origins of jihadist terrorism in the US find they’re overwhelmingly US citizens or legal residents.”

Narrowing in on fatalities caused by Muslim terrorists in the US since 9/11, the University of North Carolina’s Kurzman observed, “only one-sixth were due to immigrants and most of those, within that one-sixth, would not have been caught by ‘extreme vetting’, because they arrived as children.

“Of the seven countries still being considered [for the travel ban], there have been no fatalities at all from the United States caused by immigrants from those countries or immigrants’ children or grandchildren.”