(This story has been updated to include new information.)
The Pentagon has paused all briefings with President-elect Biden's transition team and officials from both camps are publicly at odds over why the meetings have been halted.
The news, first reported by Axios, follows a massive cyber breach that may have significant implications for national security, and also comes as President Trump continues to baselessly assert he would have won a second term if not for massive voter fraud.
Acting Defense Secretary Chris Miller said the Defense Department and the Biden team are in a "mutually agreed upon holiday pause, which begins tomorrow" and ends Jan. 1.
But Biden spokesman Yohannes Abraham contradicted Miller's statement and said he hopes the decision to stop the briefings "will be reversed."
"No, there was no mutually agreed upon holiday break," Abraham said. "In fact, we think it's important that briefings and other engagements continue during this period, as we have no time to spare and that's especially true in the aftermath of the ascertainment delay."
Transition activities did not begin until weeks after the election because Trump was challenging vote counts in several states. On Nov. 23, Trump allowed the Government Services Administration to make an official "ascertainment" that Biden won the election, which gave the green light for transition activities to begin.
Abraham also said while many DOD officials have been cooperative, the transition team has "met isolated resistance in some corners, including from political appointees within the Department of Defense."
"We were concerned to learn this week of an abrupt halt in the already limited cooperation, and we hope and expect that decision will be reversed," he said. "No department is more pivotal to our national security than the Department of Defense, and a failure to work together could have consequences well beyond January 20."
Miller, in his statement, asserted that DOD has been cooperative with Biden's team.
"As of today, we have supported 139 interview sessions [with] more than 200 DOD personnel, 161 requests for information, and disclosed thousands of pages of non-public and classified documents, exceeding prior transitions," Miller said. "At no time has the department cancelled or declined any interview."
Miller said his "key focus" over the next two weeks will be to support the Biden team's request for information on Operation Warp Speed.
"Again, I remain committed to a full and transparent transition -- this is what our nation expects, and the DOD will deliver AS IT ALWAYS HAS," he said.
Axios, meanwhile, reported that DOD sources are characterizing the decision to pause the briefings as "shocking."
Today marks the second time DOD has had to defend itself against reports that Pentagon officials are impeding the presidential transition.
A Washington Post story earlier this month said Biden's team was being blocked from touring intelligence agencies, but DOD later arranged the tours and briefings, chalking earlier problems up to procedural delays.
Miller, in his statement, said DOD since Nov. 23 has responded to 161 requests for information from the Biden team, provided 4,400 pages of controlled non-public information and 900 pages of classified information.
"We continue to schedule interviews with senior leaders and career officials," he said. "Today, we are working to reschedule approximately 20 interviews with 40 officials until after January 1."