Joe Biden was facing fresh scrutiny over his handling of government secrets on Wednesday after a second batch of classified materials was reportedly found at a location linked to him.

The White House was already on the defensive after revelations that classified documents were discovered last November in an office used by Biden after he served as US vice-president. On Tuesday he said he was “surprised to learn” of their existence.

Then came a report from the NBC News network, followed by other media outlets, that said the president’s aides had found another set of classified documents at a separate location. The classification level, number and precise location of the material was not immediately clear, NBC News added.

The allegation handed fresh ammunition to Republicans seeking to draw a false equivalence with a justice department investigation into former president Donald Trump’s mishandling of classified documents at his Mar-a-Lago residence in Florida.

Josh Hawley, a Republican senator for Missouri and ardent Trump defender, responded to the disclosure by tweeting: “Special counsel”.

Biden maintained an office at the Penn Biden Center for Diplomacy and Global Engagement, a thinktank in Washington, after he left the vice-presidency in 2017 until shortly before he launched his 2020 presidential campaign. It was affiliated with the University of Pennsylvania and continued to operate independently of the Biden administration.

Richard Sauber, special counsel to the president, has said “a small number of documents with classified markings” were discovered on 2 November 2022 in a locked closet at the centre as Biden’s personal lawyers were clearing out the offices. According to Sauber, the lawyers immediately alerted the White House counsel’s office, which notified the National Archives, which took custody of the documents the next day.

But it remains unclear why the administration waited more than two months to acknowledge the discovery of the records and what exactly they contain. Trump weighed in on his social media site, demanding: “When is the FBI going to raid the many homes of Joe Biden, perhaps even the White House?”

At a press conference in Mexico on Tuesday, Biden said he takes classified documents “seriously” and his team acted appropriately by quickly turning the documents over. “They did what they should have done. They immediately called the Archives.”

But a day later his spokesperson, Karine Jean-Pierre, faced tough questioning from a White House press corps starved of scandal since the end of the Trump presidency. She declined to say how the documents came to be at the office or when Biden was informed of their existence or provide assurances that other materials would not come to light.

“I know you all are going to have a lot of questions on this but at this time I’m not going to go beyond what the president said yesterday,” Jean-Pierre said. “I’m not going to go beyond what my colleagues from the White House counsel shared with many of you as well on Monday. I want to be prudent here and make sure that my colleagues really truly handle this issue.”

Asked why it had taken so long for the existence of the document to be disclosed, she replied: “This is under review by the Department of Justice.”

There was an unusually acrimonious exchange with Ed O’Keefe, senior White House correspondent of CBS News, who pointed out that Biden had started his tenure by acknowledging that he would make mistakes and be transparent about them. Jean-Pierre retorted: “We don’t need to have this kind of confrontation. Ask your question.”

Attorney general Merrick Garland has reportedly asked US attorney for the northern district of Illinois John Lausch – one of the few US attorneys to be held over from Trump’s administration – to review the matter after the Archives referred the issue to the department.

The situation contrasts sharply with that of Trump, who had around 300 documents with classification markings, including some that were recovered in an FBI search after his lawyers provided a sworn certification that all government records had been returned.

In November Garland appointed Jack Smith, a veteran war crimes prosecutor with a background in public corruption cases, to lead investigations into Trump’s retention of classified documents, as well as key aspects of a separate investigation regarding the January 6 attack on the US Capitol.

But such distinctions are likely to be lost for many voters, especially as Republicans and rightwing media capitalise on the apparent misstep and accuse the justice department of double standards. Reports of a second batch of documents are likely to add fuel to the fire.

Congressman Jim Jordan, chair of the House of Representatives’ judiciary committee, said the American public deserved to know earlier about the revelation of Biden’s classified documents.

“They knew about this a week before the election, maybe the American people should have known that,” he told reporters. “They certainly knew about the the raid on Mar-a-Lago 91 days before this election, but nice if on November 2, the country would have known that there were classified documents at the Biden Center.”

Congressman Mike Turner of the House intelligence committee has requested that the US intelligence community conduct a “damage assessment” of the documents found at the Penn Center.

The White House did not respond to a request for comment.