President Trump will meet with Ukrainian President Volodymyr Zelensky at the United Nations General Assembly this week, amid reports that Ukraine is the subject of a whistleblower complaint causing a standoff between Congress and the intelligence community.

Congressional Democrats have been sounding the alarm over the mysterious whistleblower report to the inspector general of the intelligence community that the Trump administration is refusing to provide to Congress. The Washington Post first reported that Ukraine was the subject of the complaint Thursday night. A source familiar with the complaint confirmed to CBS News that the conduct detailed in the complaint involves Ukraine. The source emphasized Ukraine was just "part" of the complaint, suggesting that it included more than one element/allegation.

The unidentified whistleblower filed the complaint with the intelligence community inspector general, Michael Atkinson, on August 12. The inspector general investigated the complaint and deemed it credible, forwarding it to the acting director as required, according to a letter from the inspector general released by House Intelligence Committee Chairman Adam Schiff.

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But Acting Director of National Intelligence Joseph Maguire has refused to share the complaint with Congress. Atkinson briefed lawmakers behind closed doors on Thursday, and Maguire is expected to testify in open session before the House Intelligence Committee next week after testimony this week was delayed. The Senate Intelligence Committee expects to be briefed by both about the complaint next week, according to a committee spokesperson.

The Washington Post and the New York Times reported Thursday night that a call between Mr. Trump and the newly-elected Zelensky on July 25 was the focal point of the complaint.

The Ukrainian government's readout of the call said Mr. Trump was "convinced that the new Ukrainian government will be able to quickly improve image of Ukraine, complete investigation of corruption cases, which inhibited the interaction between Ukraine and the USA."

Vice President Mike Pence met with Zelensky twice in September.

The president's personal lawyer has been pressing Ukraine to investigate Joe Biden and son Hunter Biden for corruption. In a heated interview with CNN on Thursday night, Giuliani, first said he didn't ask Ukrainian officials to investigate Joe Biden for bribery and then, less than 30 seconds later, reversed himself and said "of course I did."

He explained to host Chris Cuomo, "I found out this incredible story about Joe Biden, that he bribed the president of the Ukraine in order to fire a prosecutor who was investigating his son."

Cuomo asked Giuliani, "Did you ask the Ukraine to investigate Joe Biden?"

"No, actually I didn't," Giuliani responded. "I asked the Ukraine to investigate the allegations that there was interference in the election of 2016 by the Ukrainians for the benefit of Hillary Clinton —"

Cuomo pressed him, "You never asked anything about Hunter Biden? You never asked anything about Joe Biden?"

Giuliani replied that "the only thing I asked about Joe Biden" was to get to the bottom of how it was that the prosecutor who had been appointed to investigate Biden dismissed the case against him.

"So you did ask Ukraine to look into Joe Biden," Cuomo asked.

"Of course I did," said Giuliani.

Giuliani said he wasn't ordered by Mr. Trump to investigate Biden and didn't inform the president of his investigation until after the fact.

Hunter Biden served on the board of a Ukrainian natural gas company owned by Mykola Zlochevsky, a wealthy associate of Viktor Yanukovych, the pro-Russian Ukrainian president who was forced into exile in 2014. Zlochevsky was subsequently investigated for corruption, and a new prosecutor general, Viktor Shokin, took over the investigation in 2015, Politifact noted.

It is true that Joe Biden, while he was vice president, threatened to withhold aid from Ukraine unless it ousted Shokin, which Ukraine agreed to do. However, Shokin was perceived by the U.S. and its allies as not pursuing corruption cases aggressively enough, Politifact points out, and he was suspected of trying to protect pro-Russian interests. The case against Zlochevsky languished while Shokin was prosecutor.

Hunter Biden has said he never spoke to his father about his service on the board. Nonetheless, the younger Biden has faced widespread criticism for accepting the position while his father was vice president.

Reporting by Paula Reid, Sara Cook, Kathryn Watson, Rob Legare and Grace Segers.