WASHINGTON – President Donald Trump said Friday it "doesn't matter" if he asked the government of Ukraine to investigate Democratic opponent Joe Biden and his son, and that it should be done anyway.

"Someone ought to look into Joe Biden," Trump told reporters while declining to discuss investigations into whether he and aides are pressuring Ukraine to investigate one of his most prominent political opponents.

That question is the subject of an ongoing congressional investigation and, reportedly, the still-secret complaint of a whistleblower in the intelligence community.

Biden said in a written statement that, if true, the reports show "there is truly no bottom to President Trump’s willingness to abuse his power and abase our country. This behavior is particularly abhorrent because it exploits the foreign policy of our country and undermines our national security for political purposes."

Speaking with reporters in the Oval Office, Trump said his conversations with world leaders are “always appropriate, at the highest level always appropriate.”

Asked whether he discussed Biden in this conversation, Trump said: "It doesn’t matter what I discussed."

More:Joe Biden: Trump suggestion of wrongdoing in Ukraine not credible

The Wall Street Journal reported Friday that, in a July phone call, Trump "repeatedly pressured" Ukraine President Volodymyr Zelensky, to investigate Biden's son, who had business interests in the country. The Journal said Trump told Zelensky "about eight times to work with Rudy Giuliani, his personal lawyer, on a probe, according to people familiar with the matter."

As Democrats look at allegations that Trump and aides sought to pressure Ukraine into helping the president's re-election bid, they are also seeking details of a still-secret complaint by an unnamed intelligence official regarding the president's talks with foreign leaders.

"We're determined to do everything we can to determine what this urgent concern is," said Rep. Adam Schiff, D-Cal., chairman of the House Intelligence Committee.

House Speaker Nancy Pelosi, D-Calif., called on the Trump administration to release the complaint to lawmakers. "We must be sure," she said, "that the President and his Administration are conducting our national security and foreign policy in the best interest of the American people, not the President’s personal interest."

Biden also called on Trump to release a transcript of the telephone call in question, saying "such clear-cut corruption damages and diminishes our institutions of government by making them tools of a personal political vendetta."

While campaigning in Cedar Rapids, Iowa, Biden said accusations swirling around Hunter Biden's business interests in Ukraine, are entirely bogus and political.

"Not one single credible outlet has given credibility to these assertions – not one single one," Biden said. "So I have no comment other than the president should start to be president.”

Meanwhile, the U.S. and Ukraine governments announced that Trump and Zelensky, will meet next week at the United Nations.

Trump's relationship with Zelensky – including a July 25 phone conversation – is the subject of a congressional investigation, and perhaps part of the whistleblower complaint as well.

The Washington Post, citing unnamed people familiar with the matter, reported that "a whistleblower complaint about President Trump made by an intelligence official centers on Ukraine."

Congressional Democrats said they don't know what is in the whistleblower complaint because the Trump administration is preventing them from seeing it. Trump administration officials have declined to discuss the matter publicly.

Earlier this month, Schiff and two other Democratic House committee chairs asked the administration for a transcript of the Trump-Zelensky call, and other records related to Ukraine. In a letter to administration attorneys, lawmakers referenced news reports that Trump or his allies are urging Ukraine to investigate the business dealings of Hunter Biden.

The Democrats said they want to review "reported efforts by President Trump, the President’s personal lawyer Rudy Giuliani, and possibly others to pressure the government of Ukraine to assist the President’s reelection campaign."

They added that "a growing public record" indicates that Trump and Giuliani "appear to have acted outside legitimate law enforcement and diplomatic channels to coerce the Ukrainian government into pursuing two politically-motivated investigations under the guise of anti-corruption activity."

In a summary of the July phone call with its president, the Ukraine government said Trump expressed a desire for a "complete investigation of corruption cases, which inhibited the interaction between Ukraine and the USA."

Trump aides have promoted news stories saying that, in 2016, then-Vice President Biden threatened to withhold $1 billion in U.S. aid if Ukraine's government did not dismiss its top prosecutor, Viktor Shokin.

At the time, Biden's son Hunter was on the board of an energy company owned by a Ukraine oligarch who was being investigated by the prosecutor, who was accused by U.S. officials of ignoring corruption in his own office.

The Ukrainian Parliament eventually voted out the prosecutor.

In addition to the existing Ukraine probe, the House Intelligence Community is seeking to learn the details of the whistleblower complaint. On Thursday, it met behind closed doors with the inspector general of the intelligence community.

Schiff said the inspector general believes the allegation is serious enough to warrant transmission to Congress. But the release is being blocked by acting national intelligence director Joseph Maguire, who is scheduled to testify before the Intelligence Committee next week.

Schiff said others in the administration are also trying to hide the complaint against Trump.

"We do know that the Department of Justice has been involved in the decision to withhold that information from Congress," Schiff said. "We do not know, because we cannot get an answer to the question about whether the White House is also involved in preventing this information from coming to Congress.

"There is no privilege that covers whether the White House is involved in trying to stifle whistleblower complaints," Schiff said.

Contributing: Aamer Madhani