The US National Archives has asked representatives for former presidents and vice-presidents on Thursday to review their personal records for any classified-marked documents in their possession after a series of such discoveries at the homes of Joe Biden, Donald Trump and Mike Pence.

The archives sent letters to the presidents and vice-presidents in the previous six administrations that are covered under the Presidential Records Act, which requires materials from their time in the White House to be turned over to the agency when they leave office.

“We request that you conduct an assessment of any materials held outside of Nara [National Archives and Records Administration] to determine whether bodies of materials previously assumed to be personal in nature might inadvertently contain Presidential or Vice Presidential records,” the letters said.

The requests are understood to have gone to representatives for former presidents including Barack Obama, George W Bush and Bill Clinton, as well as former vice-presidents Dick Cheney, Al Gore and Dan Quayle, according to a source familiar with the matter.

The archives did not respond to a request for comment.

Representatives for the four former presidents have said that they had not retained any classified-marked documents after leaving the White House, though Pence himself also claimed he had returned everything to the government until a recent search of his home found otherwise.

The requests, earlier reported by CNN, come after lawyers to Biden and then Pence reported that a search of their private properties turned up classified-marked documents, months after the FBI searched Donald Trump’s Mar-a-Lago resort in August and seized about 100 such documents.

The most recent spate of discoveries started with the revelation that Biden’s personal lawyer had found a number of classified-marked documents on 2 November, when he was clearing out his office last November at the University of Pennsylvania Biden Center for Diplomacy in Washington.

Some of the documents at the UPenn Biden Center, the Guardian previously reported, included papers marked as classified at the Top Secret/Secret Compartmented Information level that were immediately reported to the National Archives, which in turn alerted the US justice department.

The attorney general, Merrick Garland, asked US attorney John Lausch on 14 November to conduct a review of the matter. After the additional papers were found late last year, Lausch recommended on 5 January that Garland appoint a special counsel to take over the inquiry.

Garland appointed Robert Hur, a top former Trump justice department official to serve as special counsel in the Biden documents case on 10 January, seeking to insulate the department from possible accusations of political conflicts after he named a special counsel to investigate Trump.

The Biden documents case last week prompted close aides to Pence to search the former vice-president’s home in Indiana out of an abundance of caution, where they found a number of classified-marked documents, Pence’s counsel Greg Jacob said in a letter to the National Archives on 18 January.

The letter added that the aide who searched the property could not specify anything more about the documents – including the content, dates and classification level, which remain unclear – because he stopped looking as soon as he saw the classified markings.

The discovery of classified-marked documents is an embarrassing development for Pence after he confidently told ABC News last year that he had not improperly removed any materials from the White House. “I did not,” Pence said in November last year.

Trump – Pence’s former boss – has been under federal investigation for more than a year over whether he wilfully retained national security documents at his Mar-a-Lago resort, and whether he obstructed efforts by the justice department to secure their return starting in May last year.

Compared with Biden, and now Pence, who moved quickly to return documents to the government, Trump’s resistance to handing over materials at his Florida property led to the justice department turning his case into a criminal investigation.

The department has typically pursued cases of mishandled classified documents criminally when they involve a combination of four aggravating factors: wilful mishandling of classified information, vast quantities of materials to suggest misconduct, disloyalty to the United States and obstruction.

The investigation into Trump touches on at least two of those elements – obstruction, where a person conceals documents with an intent to impede a government agency, and the volume of classified materials at Mar-a-Lago.