NEW YORK – President Donald Trump acknowledged Tuesday that he withheld foreign aid from Ukraine but insisted he didn't use the moneyas leverage to demand an investigation by Kiev into his top political rival, Joe Biden.

Trump said he held up the money because he wanted other countries to contribute as well – one of several explanations he and his staff have offered as the scandal around his conversations with Ukraine about Biden widened.

"Germany, France, other countries should put up money, and that has been my complaint from the beginning," he said before speaking to the United Nations General Assembly.

As Democrats pointed to the Ukraine controversy to call for impeachment hearings, Trump noted that the United States provided about $400 million in assistance this month.

"By the way," he said, "we paid that money."

The controversy began with reports that a whistleblower in the intelligence community called attention to conversations between Trump and a foreign leader. Reports surfaced over the weekend that Trump asked Ukrainian President Volodymyr Zelensky to look into allegations about the Biden family.

Trump and his personal attorney Rudy Giuliani have pushed uncorroborated claims for months that Biden as vice president sought the ouster in 2016 of Ukraine’s then-prosecutor general Viktor Shokin to stop an investigation into Burisma Group, a Ukrainian energy company where the vice president's son Hunter served on the board of directors.

The push by the vice president came alongside calls for Ukraine to get rid of Shokin from European diplomats and the U.S. State Department because international leaders said Shokin did too little to fight corruption in the Eastern European country.

The Ukrainian Parliament voted Shokin out.

The Washington Post reported that in July, Trump told his acting chief of staff, Mick Mulvaney, to hold back almost $400 million in military aid for at least a week before Trump had a phone call with Zelensky.

Trump acknowledged that the subject of Biden surfaced in the call, but he denied tying aid to an investigation of Biden. "There was no pressure put on them whatsoever," he said at the United Nations.

House Democrats stepped up calls for an impeachment investigation, saying that if Trump used congressionally approved aid meant for Ukraine to dig up dirt on a political rival, it would amount to an egregious abuse of power.

"The president of the United States may have used his position to pressure a foreign country into investigating a political opponent, and he sought to use U.S. taxpayer dollars as leverage to do it," seven freshmen House Democrats wrote in an opinion piece in The Washington Post, signaling a possible shift among Democrats in states with more moderate voters.

One of those Democrats, Rep. Elissa Slotkin, D-Mich., tweeted, "I swore an oath to protect and defend the Constitution. If true, these new allegations against the President are a threat to our national security, and constitute an impeachable offense."

At the United Nations, Trump called the impeachment talk ridiculous and politically motivated. "I'm leading in the polls," he said, and "they have no idea how to stop me. The only way they can try is through impeachment."

Trump suggested his staff would provide a "readout" of the call with Zelensky in the coming days.

His comments echoed those made Monday as he met with a succession of foreign leaders at the U.N. meeting. Trump defended his actions, blasted Biden and denounced growing Democratic impeachment threats as a new kind of "witch hunt."

Trump claimed Biden's actions and the Ukraine business interests of his son warrant investigation.

Trump said he had concerns about providing aid to Ukraine because of corruption in the country.

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House Speaker Nancy Pelosi, D-Calif., has a series of meetings Tuesday afternoon in which impeachment will be a topic.

The allegations against Trump are in a whistleblower complaint that remains secret.

Trump argued that the contents of the call were appropriate.

Some congressional Republicans, though critical of Trump's decision to discuss Biden with a foreign leader, warned against a rush to judgment.

"It is possible to do something that is wrong and not be an impeachable offense," said Sen. Marco Rubio, R-Fla. "And people around here are throwing that term around so loosely, it's lost all meaning."