The US Department of Justice has asked Mike Pence to testify in its investigation of Donald Trump’s election subversion and the former vice-president was considering the request, sources with knowledge of the situation have told the Guardian.

Last week, Pence said he would not testify to the House January 6 committee, telling CBS: “Congress has no right to my testimony on separation of powers under the constitution of the United States. And I believe it will establish a terrible precedent for the Congress to summon a vice-president of the United States to speak about deliberations that took place at the White House.”

Pence also said the committee, made up of seven Democrats and two Republicans, was too partisan. The chair and vice-chair of the panel, Bennie Thompson and Liz Cheney, rejected that charge.

The New York Times first reported the news of the approach to Pence and said he recognised that the Department of Justice investigation could not be dismissed.

The newspaper said the request to Pence was made before the attorney general, Merrick Garland, announced last Friday the appointment of a special counsel to oversee the justice department investigation.

Garland said the appointment of the career prosecutor Jack Smith would not slow the investigation of Trump’s attempt to stay in power despite losing the 2020 election to Joe Biden, culminating in the deadly Capitol attack on 6 January 2021.

Smith will also oversee the investigation of Trump’s retention of White House records.

Trump has tried to stop other senior aides testifying to the Department of Justice, claiming executive privilege. Many aides have been served with subpoenas.

Pence and the Department of Justice did not immediately comment on the Times report.

On Sunday, Pence was asked if he thought Trump committed a crime in connection with the events of January 6, when some Trump supporters who attacked the Capitol chanted “Hang Mike Pence”.

Pence told NBC: “I don’t know if it is criminal to listen to bad advice from lawyers.”

Eyeing his own presidential run in 2024, Pence must pursue a balancing act as he seeks to distance himself from Trump while appealing to Republican voters.

In that spirit he has published a memoir, So Help Me God, which deals in detail with his version of events during his time at Trump’s side. The book includes an extensive account of Pence’s role in and views of Trump’s attempts to stay in office.

Pence ultimately refused to block certification of electoral college results, a process over which he presided. Trump, he writes, said he was “too honest” to take part in a plot based on claims of widespread electoral fraud. But Pence also says Republicans were right to lodge objections to results in key states, as it “meant we would have a substantive debate”.

Either way, it seems Trump would have reason to fear testimony to the Department of Justice by his former vice-president. In his book and in interviews to promote it, Pence has made clear he blames Trump for the Capitol riot.

Earlier this month, Pence told ABC Trump’s words and actions “angered me”.

“But I turned to my daughter who was standing nearby. And I said, ‘It doesn’t take courage to break the law. It takes courage to uphold the law.’ The president’s words were reckless. It’s clear he decided to be part of the problem.”