Washington (CNN) House Speaker Nancy Pelosi on Wednesday said she thinks President Donald Trump is "scared" of the impeachment inquiry launched by the House of Representatives because he "knows the argument can be made against him."

"I think the President knows the argument that can be made against him and he's scared, and so he's trying to divert attention from that to where (he's) standing in the way of legislation," Pelosi said in an interview with ABC News' George Stephanopoulos on Wednesday.

Pelosi's comments came after a weekly press briefing with House Intelligence Committee Chairman Adam Schiff. The pair, along with other House committees, have led House Democrats' escalating impeachment inquiry into Trump's July 25 call with Ukrainian President Volodymyr Zelensky, as well as the holding up of Ukrainian foreign aid.

A White House-released transcript of the call revealed Trump asked Zelensky to investigate Joe Biden and his son, Hunter -- though there is no evidence of wrongdoing by either Biden. A separate whistleblower complaint alleges Trump abused his official powers "to solicit interference" from Ukraine in the upcoming 2020 election, and that the White House took steps to cover it up. Trump has denied doing anything improper.

Asked Wednesday if she heard "fear" in Trump's voice during her conversation with him hours before formally announcing the House's impeachment inquiry, Pelosi said she noted the President's "surprise."

"I saw the surprise in his voice that he didn't understand that I thought what he did was wrong, that he was undermining our national security, that he was undermining our Constitution by his actions and he was undermining the integrity of our elections," she said.

Schiff warned the Trump administration against interfering with the probe.

He told reporters Wednesday that "any effort by the Secretary, by the President, or anyone else, to interfere with the Congress' ability to call before it relevant witnesses will be considered as evidence of obstruction of the lawful functions of Congress."

"More than that it will allow an adverse inference to be drawn as to the underlying facts," Schiff added.