Former Vice President Joe Biden said Tuesday that if President Donald Trump stonewalls Congress's requests for information about Trump's call with Ukraine's president and other issues, Trump "will leave Congress in my view no choice but to initiate impeachment."

"That would be a tragedy, but a tragedy of his own making," the Democratic presidential candidate Biden said.

"It's time for the Congress to fully investigate the conduct of this president," Biden said.

Biden made that statement on the heels of reports that Trump held up military aid to Ukraine shortly before a phone call with that country's president, during which Trump talked about Biden and his son, Hunter Biden.

An increasing number of Democrats in the House are calling for impeachment proceedings to begin against Trump because of suspicions he pressured Ukraine's leader to investigate Biden and Hunter Biden, who was on the board of a Ukraine gas company, in exchange for the release of $400 million in aid.

Trump denies that he pressured Ukrainian President Volodymyr Zelensky to investigate the Bidens during their July call, but on Tuesday confirmed reports that he had blocked the release the aide. He said he did so in order to get European countries to contribute to the aid package.

But Trump and his personal lawyer Rudy Giuliani have both urged Ukraine to probe the Bidens.