President Donald Trump speaks during an event on healthcare prices in the Roosevelt Room of the White House. File photo: AP Photo/ Evan Vucci.

Washington - U.S. President Donald Trump on Monday indicated publicly for the first time that he might be willing to testify in the impeachment inquiry over his dealings with Ukraine "even though I did nothing wrong."

Democrats leading the impeachment process in the U.S. House of Representatives have not formally called Trump as a witness in the inquiry into whether he used foreign policy to try to get Ukraine to investigate domestic political opponent Joe Biden.

During former U.S. Special Counsel Robert Mueller's investigation of Russian interference in the 2016 U.S. election, Trump said he was willing to testify in person but ultimately did not speak to Mueller. Instead, after extensive negotiations, Trump provided written answers to questions from Mueller's office.

Denying any wrongdoing, the Republican president has railed on Twitter and elsewhere against the impeachment inquiry and attacked witnesses by name.

House Speaker Nancy Pelosi, a Democrat, said on Sunday in a CBS interview that Trump has every opportunity to present his case, including coming before intelligence committee hearings.

"Even though I did nothing wrong, and don't like giving credibility to this No Due Process Hoax, I like the idea & will, in order to get Congress focused again, strongly consider it!" Trump said on Twitter.

At the heart of the inquiry is a July 25 phone call in which Trump asked Ukrainian President Volodymyr Zelenskiy to open a corruption investigation into former U.S. Vice President Biden and his son, Hunter Biden, and into a discredited theory that Ukraine, not Russia, meddled in the 2016 U.S. election.

The public phase of hearings shifts into higher gear this week when a parade of officials will face questioning by Democratic lawmakers seeking details that could link Trump to a pressure campaign against Ukraine.

Eight more witnesses are due to testify in the second week of the televised hearings. They include Gordon Sondland, the U.S. ambassador to the European Union, whose direct interactions with Trump are likely to be a main focus in the investigation of whether the president made security aid to Ukraine contingent on it agreeing to dig up dirt on Biden, who is a leading contender for the Democratic nomination to take on Trump in 2020.

Several witnesses testified last week that they were alarmed over the pressure tactics used against Ukraine, as well as the role of Trump’s personal lawyer, Rudy Giuliani.

The hearings could pave the way for the House to approve articles of impeachment - formal charges - against Trump. That would lead to a trial in the Senate on whether to convict Trump and remove him from office. Republicans control the Senate and have shown little support for Trump's removal.

House Speaker Pelosi, in her interview on CBS's "Face the Nation" said: "The president could come right before the committee and speak all the truth that he wants if he wants to take the oath of office ... or he can do it in writing. He has every opportunity to present his case."

The latest round of hearings will stretch from Tuesday to Thursday before the House Intelligence Committee. Democrats are looking into whether Trump abused his power in part by withholding $391 million in aid to Ukraine as leverage to get Kiev to investigate Biden. The money, approved by the U.S. Congress to help U.S. ally Ukraine combat Russia-backed separatists, was later provided.

At the first impeachment hearing last Wednesday, Republicans repeatedly blasted Democrats for not calling an anonymous whistleblower to testify publicly or behind-closed doors. The whistleblower account of the July 25 call led to Democrats opening the inquiry.

"There's one witness, one witness that they won't bring in front of us, they won't bring in front of the American people, and that's the guy who started it all, the whistle-blower," Republican Jim Jordan said on Nov. 13.

Democrat Peter Welch responded at the time, "I would be glad to have the person who started it all come in and testify. President Trump is welcome to take a seat right there."

Reuters