The families of hundreds of 9/11 victims wrote a scathing letter to President Biden demanding that he fulfill his campaign pledge to declassify government evidence that links Saudi Arabia to the attack or risk being not welcome at memorial events.

"Six months ago the 9/11 community had great hopes that President Joe Biden would be the long lost champion of those directly affected by this murderous attack on our nation, finally placing the values of truth, justice, and accountability before the interests of the Kingdom of Saudi Arabia," the signers wrote.

The Department of Justice responded in a statement Monday, pledging to work toward declassifying information on the attacks.

About 1,800 family members of 9/11 victims, survivors, and first responders signed the letter, which pointed out that Biden vowed during the campaign to direct his attorney general to "personally examine the merits of all cases" in which the government has invoked state secrets and "to err on the side of disclosure in cases where, as here, the events in question occurred two decades or longer ago."

Also during the campaign, Biden penned a letter to a representative of the families, admitting that they were "right to seek full truth and accountability."

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"The loss endured by the 9/11 Families on that horrible day in 2001 is incalculable. Nothing I can say can compensate for their loss. I hope that your work in pursuit of justice and accountability can help bring them some small degree of closure," Biden said in the letter.

The letter comes ahead of next month's 20th anniversary of the attacks, with families saying they may not welcome Biden to events and memorials to the attack if he does not declassify the information.

"As we approach the 20th anniversary of 9/11, and having been used as a political bargaining chip for two decades, our patience has expired," the letter said.

"These documents involve a terrorist attack that occurred 20 years ago, and there is no justification to withhold them," said Brett Eagleson, an advocate for 9/11 families  who also lost his father to the attacks. "We hope the Biden administration finally provides the information our families have waited to receive for 20 years, so we can stand together with the President at Ground Zero on 9/11."

The families are seeking evidence from the bipartisan 9/11 Commission that implicates Saudi Arabian officials who supported the attacks. The letter expressed frustration that previous administrations have "actively sought to keep this information secret."

White House Press Secretary Jen Psaki said on Friday that the administration has held several meetings with various 9/11 victims groups about the requests and told reporters that the families "will continue to be a priority."

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"He remains committed to that pledge he made during the campaign," Psaki said. "Of course, any steps would be taken by the Department of Justice."

Eagleson made clear that the families' ultimatum to Biden was in no way partisan, pointing out that the group had also met with former President Donald Trump and that he had led families to believe that declassification of the evidence was "very, very imminent."

"President Trump led us to believe that he was going to declassify the documents. We were talking to the administration all along and they slow-played us and hoodwinked us," Eagleson said. "[With] the 20-year anniversary, you get all sorts of attention on this subject … The families are literally at their wit’s end. Whether it’s Trump in office, whether it’s Obama in office, or whether it’s Biden in office, we would have sent this letter." 

In its letter on Monday, the DOJ said that the FBI had recently concluded an investigation that examined 9/11 hijackers and potential co-conspirators, and that it would work to see if information could be disclosed. "The FBI will disclose such information on a rolling basis as expeditiously as possible," the DOJ said.

Biden praised the DOJ's action, saying his administration is "committed to ensuring the maximum degree of transparency under the law."

Eagleson expressed skepticism after Biden's statement. "We have heard many empty promises before," he told the Associated Press.