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CNN —  

Amid the ongoing impeachment inquiry into President Donald Trump and his administration’s actions regarding Ukraine, the Pentagon’s chief legal officer has requested that Defense Department agencies identify, preserve and collect any and all documents relating to the provision of security assistance to Kiev.

“I write to request your assistance and cooperation in identifying, preserving, and collecting documents and other records regarding the (Ukraine Security Assistance Initiative) and in responding to anticipated requests for such materials,” Paul Ney, the General Counsel of the Department of Defense, wrote in a memo Thursday to various agencies and services within the Pentagon.

The Ukraine Security Assistance Initiative is the program which included the $250 million in military aid to Ukraine that the Trump Administration froze in June, a freeze that baffled multiple US and Ukrainian officials and has led to accusations that the administration was seeking to leverage that assistance to compel the new government in Kiev to investigate Trump’s political rival, former Vice President Joe Biden and his son Hunter Biden.

There is no evidence of wrongdoing by Joe or Hunter Biden.

The chief spokesman for the Pentagon called the action to preserve records relating to Ukraine “routine.”

“With regard to the general counsel memo, my understanding is this is a fairly standard practice, that when there’s a significant level of congressional or (Inspector General) interest in – in a matter, for the department to take steps, proactively, to ensure that – that these materials are available. So to me, I think it seems to be a fairly routine but proactive measure that we’re taking,” the Assistant to the Secretary of Defense for Public Affairs, Jonathan Hoffman, said at a press briefing on Thursday.

Late last month a group of seven Democratic senators wrote a letter to the Department of Defense’s Office of Inspector General requesting that it mount an investigation into why the Ukraine military aid was held up.

At the time, Illinois Democrat Sen. Dick Durbin tweeted that “the delay raises questions about whether DoD officials were involved in any scheme to target a political opponent.”

A spokesperson for the Inspector General’s office told CNN that it had “received Senator Durbin’s letter and are reviewing the request to investigate.”

Four months after the aid to Ukraine, which included .50 caliber sniper rifles and grenade launchers, was frozen, it is still unclear exactly why Trump ordered it to be held up.

The Pentagon had already announced the plan to provide the millions of dollars in military aid to Ukraine, and in May, the Department of Defense and the State Department had notified congressional oversight committees that aid to Ukraine was ready for distribution.

The grab bag of explanations the administration has offered for the hold up – and the President’s continued fixation on the Biden family – has fueled suspicion that the delay was politically motivated.

At least one US diplomat, the chargé d’affaires in Ukraine, Bill Taylor, appeared to see a connection between the proposed Biden investigations and the security assistance, calling such a linkage “crazy” in a series of recently revealed text messages between him and several other US diplomats involved in Ukraine issues.

Hoffman also said that no one from the Defense Department was on a the July phone call between Trump and Ukraine’s President Volodymyr Zelensky, where according to a rough transcript released by the White House Trump asked for a favor after Zelensky requested that the US allow Kiev to purchase additional Javelin anti-tank missiles.

On Thursday the State Department announced that it had approved a potential sale of 150 additional Javelin missiles to Ukraine, a sale that the top US military officer in Europe, Gen. Tod Wolters, told reporters at the Pentagon that he supported.

CNN’s Barbara Starr and Sara Murray contributed to this report.