President-elect Joe Biden is warning of massive damage done to the national security apparatus by the Trump administration and “roadblocks” in communication between agency officials and his transition team that could undermine Americans’ security.

Speaking on Monday in Wilmington, Delaware, Mr Biden said his team had faced “obstruction” from the “political leadership” at the Defence Department and the Office of Management and Budget as they have sought necessary information to continue the transition of power.

“Right now we just aren’t getting all the information that we need from the outgoing administration in key national security areas. It’s nothing short, in my view, of irresponsibility,” Mr Biden said.

He warned his team needed “full visibility” into the budget process at the Defence Department “in order to avoid any window of confusion or catch-up that our adversaries may try to exploit”.

He also said they need “a clear picture of our force posture around the world and of our operations to deter our enemies”.

Mr Biden’s remarks came after he was briefed by members of his national security and defence teams and advisers, including his nominees for secretary of State, Defence and Homeland Security, as well as his incoming national security adviser.

The president-elect said his team found that agencies “critical to our security have incurred enormous damage” during President Donald Trump’s time in office.

“Many of them have been hollowed out in personnel, capacity and in morale,” he said.

“All of it makes it harder for our government to protect the American people, to defend our vital interests in a world where threats are constantly evolving and our adversaries are constantly adapting.”

Mr Trump has still refused to concede an election he lost by more than seven million votes, and his administration did not authorise official cooperation with the Biden transition team until November 23 – 20 days after the election.

Mr Biden and his aides warned at the time the delay was hampering their ability to craft their own vaccine rollout plan, but have since said cooperation on that and other issues related to Covid-19 has improved.

Last week, however, Mr Biden himself said the Defence Department “won’t even brief us on many things” and suggested because of this, he did not have a complete understanding of the full scope of the recent cyberhack that breached numerous government systems.

Pentagon officials pushed back on Mr Biden’s accusations. Acting Defence Secretary Christopher Miller said in a statement the department had conducted 164 interviews with more than 400 officials, and provided more than 5,000 pages of documents, which is “far more than initially requested by Biden’s transition team”.

On Monday, Mr Biden said his team was still gathering information about the extent of the cyberhack, but described the need to “modernise” America’s defence to deter future such attacks, “rather than continuing to over-invest in legacy systems designed to address the threats of the past”.

Mr Biden also spoke at length about the need to rebuild global alliances, which he said were necessary to combat climate change, address the pandemic and prepare for future epidemics, and confront the growing threat posed by China.

“Right now, there’s an enormous vacuum. We’re going to have to regain the trust and confidence of a world that has begun to find ways to work around us or without us,” he said.