Lawyers for Joe Biden found more classified documents at his home in Wilmington, Delaware, than previously known, the White House acknowledged on Saturday.

The White House lawyer Richard Sauber said in a statement that a total of six pages of classified documents were found during a search of Biden’s private library. The White House had said previously that only a single page had been found there.

The latest disclosure is in addition to the discovery of documents found in December in Biden’s garage and in November at his former offices at the Penn Biden Center in Washington, from his time as vice-president.

Sauber said in a statement on Saturday that Biden’s personal lawyers, who did not have security clearances, had stopped their search after finding the first page on Wednesday evening. Sauber found the remaining material on Thursday, as he was facilitating their retrieval by the Department of Justice (DoJ).

“While I was transferring it to the DoJ officials who accompanied me, five additional pages with classification markings were discovered among the material with it, for a total of six pages,” Sauber said. “The DoJ officials with me immediately took possession of them.”

Sauber has previously said that the White House was “confident that a thorough review will show that these documents were inadvertently misplaced, and the president and his lawyers acted promptly upon discovery of this mistake”.

Sauber’s statement did not explain why the White House waited two days to provide an updated accounting of the number of classified documents. The White House is already facing scrutiny for waiting more than two months to acknowledge the discovery of the initial group of documents at the Biden office.

The latest development appears to bring the total number of documents marked classified and found at Biden’s home and former office to at least 20.

The trove is understood to include material categorized as top secret, among approximately 10 documents discovered at the University of Pennsylvania’s Biden Center for Diplomacy, a thinktank in the capital named after him, a federal law enforcement official familiar with the investigation into the discoveries told CBS News on Saturday.

The latest revelations prompted Andrew Weissmann, former federal prosecutor and senior member of the special counsel Robert Mueller’s team that investigated Donald Trump’s links with Moscow during his 2016 presidential election campaign, to tweet: “This may explain why the WH [White House] has not been transparent with the public about exactly what docs were found.”

He did not elaborate but, like other analysis, previously had drawn a clear distinction between the situation with documents retained from Biden’s time and Donald Trump’s hoarding of boxes of secret documents from his presidency, despite federal requests for all material to be returned, which prompted the FBI to raid his Florida residence last summer.

Biden’s legal team voluntarily turned the documents found over to federal officials after they were discovered last November.

“Let’s remember that what we are (correctly) asking the current WH to do – be as transparent as possible about what happened and when – is something Trump has not done at all, to this day, with respect to the MAL [Mar-a-Lago] docs, other than put out a series of lies,” Weissman tweeted on Thursday.

Trump and Biden are now both under investigation by separate special counsels at the request of the Department of Justice. House Republicans, now in control of the lower chamber of Congress, on Friday announced an investigation of Biden by the judiciary committee.

The current White House explanation for Biden’s situation, offered by Sauber, is that the special counsel’s inquiry “will show that these documents were inadvertently misplaced” – a “mistake” with the nation’s secrets, after the former vice-president’s office was hastily packed up at the end of the Obama administration, just before Trump took office.

Richard Painter, the top ethics official in the George W Bush administration, called such behavior “incredibly careless and really quite shocking” but emphasized that Biden probably would avoid the criminal issues looming over Trump because there is so far no sense that Biden intentionally mishandled classified records.

“You never just pack stuff up and cart it out of there,” Painter said. Aides and lawyers are supposed to carefully sift through what are official records that are property of the National Archives and personal records that may be removed.

“To say nothing of classified documents which have these distinctive markings on them. It’s a serious national security breach,” he added.

Later on Saturday afternoon, Weissmann retweeted a sarcastic post from George Conway, founder of the anti-Trump Republican group the Lincoln Project and married to the former Trump senior White House adviser Kellyanne Conway, drawing contrast between Trump’s and Biden’s cases.

“What a crazy approach, looking for documents and immediately turning them over to the government. Why not instead declassify the documents in your head and spend the next year stonewalling, lying and obstructing justice? Weak. Sad,” tweeted Conway, who was quote-tweeting a post with the Biden White House statement, and mocking Trump’s prior claims that he had declassified material later found at Mar-a-Lago “by thinking about it”.