The Trump administration pushed back Tuesday in the wake of multiple reports that the White House froze millions in aid to Ukraine shortly before President Trump pressured the country's leader to investigate Joe Biden and his son Hunter.

The reports coincided with a renewed round of calls, including from more centrist Democrats, for a formal impeachment inquiry. Those calls came a day after House Speaker Nancy Pelosi suggested she is opening the door to that route if the administration continues to withhold a whistleblower complaint apparently related to Trump's Ukraine discussions.

FLURRY OF HOUSE DEMOCRATS BACK IMPEACHMENT INQUIRY, AMID BOMBSHELL REPORTS TRUMP WITHHELD UKRAINE AID

Multiple administration sources confirmed to Fox News on Tuesday that the Office of Management and Budget indeed told the State Department and Department of Defense in July that it was putting a hold on nearly $400 million in aid to Ukraine.

But administration sources told Fox News that the reason for the freeze on Ukrainian aid was tied to concerns about corruption. Sources said that Trump wanted to be confident that the incoming administration of Volodymyr Zelensky was going to take steps to end corruption before releasing the funding.

The aid to Ukraine also, according to sources, came up in the context of other countries and questions about whether they were paying their share.

Trump, on the sidelines of the United Nations General Assembly later Tuesday, insisted he only sought to hold up the Ukraine aid because he “wanted other countries to pay.”

“There was no quid pro quo,” he said. “There was no pressure applied, nothing.”

The White House’s decision to release the funding ultimately was made in mid-August, after Sen. Rob Portman, R-Ohio, called the president and said that Ukraine desperately needed the aid, according to administration sources.

The White House, at the time, was also up against an appropriation “impoundment” deadline, which meant the money would either have to be spent, or impounded. The White House would have been forced to go to court to justify the impoundment, which sources said it did not want to do.

The White House, though, has denied the allegations that the freezing of the Ukrainian aid was tied to allegations that the president asked Zelensky to investigate the Bidens.

“The media pushed the Russia lie for almost three years with no evidence, and now they are doing it all over again,” White House Deputy Press Secretary Hogan Gidley told Fox News. “These allegations are completely false, but because the media wants this story to be true so badly, they’ll once again manufacture a frenzy and drive ignorant, fake stories to attack this President.”

In remarks to reporters at the United Nations Monday, Trump also denied linking the aid money to Ukraine’s investigative actions.

“No, I didn’t—I didn’t do it,” Trump said, also calling the Biden’s actions in Ukraine a “disgrace,” and adding: “It’s very important to talk about corruption…Why would you give money to a country that you think is corrupt?”

But Democrats are concerned the president may have essentially withheld money to Ukraine as leverage to seek an investigation concerning the Bidens -- which is now prompting renewed impeachment calls.

The furor began after a whistleblower complaint was reported last week that involved allegations that Trump made an unspecified “promise” to Zelensky. A person familiar with the situation told Fox News that the whistleblower in question did not have “firsthand knowledge” of Trump’s conversation with Zelensky, but Democrats want to see the complaint.

SOURCE TO FOX NEWS: WHISTLEBLOWER HAD NO FIRST-HAND KNOWLEDGE OF TRUMP CALL

Joe Biden has acknowledged that during the Obama administration, he successfully pressured Ukraine to fire its top prosecutor, Viktor Shokin, who was investigating the natural gas firm Burisma Holdings where Hunter Biden was on the board. Trump and his allies have openly voiced concerns about the now-Democratic presidential candidate's role.

Nevertheless, Democrats have used the reports and new allegations against the president to press forward—even as it risks backfiring by exposing potential wrongdoing by Biden.

Late Monday night, a slew of key swing-district Democrats publicly offered their support for opening a formal impeachment inquiry. Seven centrist Democratic freshmen lawmakers who served in the military and national security announced in an op-ed in The Washington Post that if Trump pressured Zelensky to investigate the Bidens for political benefit, it’s impeachable. The lawmakers included Reps. Gil Cisneros of California, Jason Crow of Colorado, Chrissy Houlahan of Pennsylvania, Elaine Luria of Virginia, Mikie Sherrill of New Jersey, Elissa Slotkin of Michigan and Abigail Spanberger of Virginia.

The Democrats wrote in The Washington Post they "do not arrive at this conclusion lightly."

“These allegations are stunning, both in the national security threat they pose and the potential corruption they represent," the lawmakers said. “These new allegations are a threat to all we have sworn to protect. We must preserve the checks and balances envisioned by the Founders and restore the trust of the American people in our government. And that is what we intend to do.”

Also, later Monday night, Hawaii Democratic Sen. Brian Schatz and Michigan Democratic Rep. Debbie Dingell endorsed an impeachment inquiry. Such an inquiry would not be an impeachment vote, but rather an investigative process that could lead to actual impeachment.

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There are now 154 House Democrats who have signaled strong support for possible impeachment proceedings. (235 Democrats and 198 Republicans are in the House, with one independent -- and a majority would be required to successfully impeach the president. An unlikely two-thirds vote in the GOP-controlled Senate would be needed to convict and remove the president.)

Fox News' Gregg Re contributed to this report.