WASHINGTON, Jan. 15 (Xinhua) -- U.S. Secretary of Health and Human Services Alex Azar is resigning on Jan. 20, citing the violence on Capitol Hill last week, according to his resignation letter leaked Friday.

In the letter dated Jan. 12, Azar said "the actions and rhetoric following the election, especially during the past week, threaten to tarnish" the legacies of the administration of President Donald Trump, and "the attacks on the Capitol were an assault on our democracy and on the tradition of peaceful transitions of power."

"I implore you," Azar told Trump in the letter, "to continue to condemn unequivocally any form of violence, to demand that no one attempt to disrupt the (President-elect Joe Biden's) inaugural activities in Washington or elsewhere."

The latest Trump Cabinet member to quit in the aftermath of the violence by the president's supporters, Azar's move followed those of Transportation Secretary Elaine Chao, Education Secretary Betsy DeVos, and Acting Secretary of Homeland Security Chad Wolf.

Azar's resignation came at such a critical moment that despite the Trump administration's recently announced plan to release all the coronavirus vaccines originally in reserve for second shots, multiple U.S. media reported that such reserves actually no longer existed.

The administration stopped stockpiling second doses of the Pfizer-BioNTech vaccine at the end of last year, said the reports, citing state and federal officials briefed on vaccine distribution. Shipping of the last reserve doses of the Moderna vaccine supply began over the weekend.

Both the Pfizer and the Moderna vaccines are on two-dose regimens.

The revelation appeared to contradict Azar's statement Tuesday at an Operation Warp Speed briefing, where he said "the administration would be "releasing the entire supply for order by states, rather than holding second doses in reserve." Operation Warp Speed is the Trump administration's initiative for vaccine distribution.

Azar tried to clarify those remarks during an interview with NBC News on Friday, saying "we now have enough confidence that our ongoing production will be quality and available to provide the second dose for people, so we're not sitting on a reserve anymore."

The confusion Azar and other federal officials brought about has outraged state governors tasked with distributing the federally-supplied vaccines as they are scrambling to find enough vials.

"I am demanding answers from the Trump Administration," Oregon's Democratic governor, Kate Brown, tweeted Friday. "I am shocked and appalled that they have set an expectation on which they could not deliver, with such grave consequences. This is a deception on a national scale."