In that statement, Pentagon press secretary Alyssa Farah announced that James Anderson, the current senior official Performing the Duties of the Deputy Under Secretary of Defense for Policy, will take over Rood's responsibilities until a permanent replacement is appointed by the president and confirmed.
The request for Rood's resignation came after senior national security leaders lost confidence in the official, who oversees the Pentagon's cooperation with United States allies, the report said.
The certification undercut Trump's argument in an impeachment probe against him that he had sought to withhold aid to Ukraine due to rampant graft there, and not to pressure Ukrainian leaders to investigate political rival Joe Biden, as alleged by House Democrats.
In President Trump's impeachment saga, Rood was the official who initially certified to Congress that Ukraine's reforms justified sending Kyiv $250 million in military aid in May 2019.
TPM's inquiries with the National Security Council and the Pentagon were not immediately returned.
Rood was instrumental in reversing the Pentagon's initial opposition to that measure, proposed by the Commerce Department, which would have expanded the scope of items made overseas that the USA could have blocked from being sold to Huawei, sources familiar with the matter said.
John Rood resigned Wednesday, saying he was leaving at Trump's request.
"It's my understanding from Secretary [Mark] Esper that you requested my resignation", Rood said. And he said: "I have certified that the government of Ukraine has taken substantial actions to make defense institutional reforms for the objective of decreasing corruption and making other improvements".
Asked about Rood's resignation, chief Pentagon spokesman Jonathan Hoffman declined to speculate on the reason for Trump's decision.
'The president has the opportunity and the ability to have the team that he wants to have in policy positions, ' Hoffman said at news conference.
He could not say whether Esper recommended to the president that Rood be removed and referred back to the resignation letter.
He later told reporters: "In the weeks after signing the certification I did become aware that the aid had been held".
Pentagon press secretary Alyssa Farah said James Anderson, who is now serving as the deputy for policy, will take over the job until a permanent replacement is appointed by the president and confirmed.
"John has played a critical role on a wide range of DoD issues including modernizing our nuclear deterrence capability, efforts to increase burden sharing by our North Atlantic Treaty Organisation allies, our Missile Defense Review and implementing the National Defense Strategy". He has also held senior roles with major defense contractors Lockheed Martin and Raytheon.