Michael Duffey, National Security Associate Director, asked "based on guidance" received in light of the Trump Administration's revised assistance plan to Ukraine, that Pentagon officials withhold aid in July, the emails made available on Sunday by the non-profit Center for Public Integrity revealed.
"Given the sensitive nature of the request, I appreciate your keeping that information closely held to those who need to know to execute direction," reads Duffey's email to Pentagon official Elaine McCusker, dated July 25.
The documents were obtained by the non-profit following a judge order and show the call between the rulers occurred between 9.03 a.m. and 9.33 a.m. on July 25, 91 minutes before Duffey's 11.04 a.m. email - which also appears in another batch at 3.03 p.m., Efe news reported.
This development comes after the Democrat-controlled House of Representatives voted on December 18 to pass two articles of impeachment against Trump, making him the third president to be indicted in the country's history.
The process was triggered by a September leak from inside the White House about a controversial favour the President allegedly asked the Ukrainian leader during the July telephone conversation.
The leak, attributed to a CIA agent assigned to the White House to inform intelligence services about a July telephone conversation between Trump and Zelensky, encouraged Democrats to push the process forward.
In that call, Trump pressured Zelensky to investigate his political rival and former Vice President, Democrat Joe Biden - currently a candidate for his party in the 2020 US election - and his son Hunter for alleged corruption in Ukraine.
The next step in the impeachment saga following the House votes, there will be a trial in the Republican-controlled Senate next month.
Trump officially became the third US President to be impeached after Andrew Johnson and Bill Clinton.
( With inputs from IANS )